Localization of phosphorylated ERK/MAP kinases to mitochondria and autophagosomes in Lewy body diseases

IGF-1 inhibits MPTP/MPP+-induced autophagy on dopaminergic neurons through the IGF-1R/PI3K-Akt-mTOR pathway and GPER

Autophagy dysfunctions are involved in the pathogenesis of Parkinson's disease (PD). In the present study, we aimed to evaluate the involvement of G protein-coupled estrogen receptor (GPER) in the inhibitory effect of insulin-like growth factor-1 (IGF-1) against excessive autophagy in PD animal and cellular models. 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treatment significantly induced mouse movement disorder and decreased the protein level of tyrosine hydroxylase (TH) in the substantia nigra (SN) and dopamine (DA) content in striatum. Along with the dopamine neuron injury, we observed significant upregulations of microtubule-associated light chain-3 II (LC3-II) and α-synuclein as well as a downregulation of P62 in MPTP-treated mice. These changes could be restored by IGF-1 pretreatment. Cotreatment with IGF-1R antagonist JB-1 or GPER antagonist G15 could block the neuroprotective effects of IGF-1. 1-Methy-4-phenylpyridinium (MPP⁺) treatment could also excessively activate autophagy along with the reduction of cell viability in SH-SY5Y cells. IGF-1 could inhibit the neurotoxicity through promoting the phosphorylation of Akt and mammalian target of rapamycin (mTOR), which could also be antagonized by JB-1 or G15. These data suggest that IGF-1 inhibits MPTP/MPP⁺-induced autophagy on dopaminergic neurons through the IGF-1R/PI3K-Akt-mTOR pathway and GPER.

HOTAIR drives autophagy in midbrain dopaminergic neurons in the substantia nigra compacta in a mouse model of Parkinson's disease by elevating NPTX2 via miR-221-3p binding

Parkinson’s disease (PD) is a neurodegenerative disorder characterized by progressive cell loss, largely confined to mesencephalic dopamine neurons of the substantia nigra. This study investigated the functional relevance of the HOX transcript antisense intergenic RNA (HOTAIR)/microRNA-221-3 (miR-221-3p)/neuronal pentraxin II (NPTX2) axis in the process of dopaminergic neuron autophagy using PD mouse models. The PD mouse models were established by intraperitoneal injection of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyrindine (MPTP), while PD cell model was constructed by pretreatment with 1-methyl-4-phenylpyridinium (MPP⁺). The expression of HOTAIR was then examined using RT-qPCR. In addition, the interactions between HOTAIR, miR-221-3p, and NPTX2 were detected through RIP and dual-luciferase reporter gene assays. CCK-8 assay was performed to measure cell viability, and the expression of autophagy-related genes was determined using Western blot analysis. HOTAIR was found to be significantly expressed in the substantia nigra compact tissues and MN9D cells following PD modeling. HOTAIR could bind to miR-221-3p and elevate the NPTX2 expression, which resulted in diminished cell viability and enhanced autophagy of dopaminergic neurons both in vitro and in vivo. In summary, down-regulation of HOTAIR could potentially inhibit the autophagy of dopaminergic neurons in the substantia nigra compacta in a mouse model of PD, thus saving the demise of dopaminergic neurons.

Autophagy in Parkinson's Disease

Impaired protein homeostasis and accumulation of damaged or abnormally modified protein are common disease mechanisms in many neurodegenerative disorders, including Parkinson's disease (PD). As one of the major degradation pathways, autophagy plays a pivotal role in maintaining effective turnover of proteins and damaged organelles in cells. Several decades of research efforts led to insights into the potential contribution of impaired autophagy machinery to α-synuclein accumulation and the degeneration of dopaminergic neurons, two major features of PD pathology. In this review, we summarize recent pathological, genetic, and mechanistic findings that link defective autophagy with PD pathogenesis in human patients, animals, and cellular models and discuss current challenges in the field.

The process of Lewy body formation, rather than simply α-synuclein fibrillization, is one of the major drivers of neurodegeneration

Parkinson's disease (PD) is characterized by the accumulation of misfolded and aggregated α-synuclein (α-syn) into intraneuronal inclusions named Lewy bodies (LBs). Although it is widely believed that α-syn plays a central role in the pathogenesis of PD, the processes that govern α-syn fibrillization and LB formation remain poorly understood. In this work, we sought to dissect the spatiotemporal events involved in the biogenesis of the LBs at the genetic, molecular, biochemical, structural, and cellular levels. Toward this goal, we further developed a seeding-based model of α-syn fibrillization to generate a neuronal model that reproduces the key events leading to LB formation, including seeding, fibrillization, and the formation of inclusions that recapitulate many of the biochemical, structural, and organizational features of bona fide LBs. Using an integrative omics, biochemical and imaging approach, we dissected the molecular events associated with the different stages of LB formation and their contribution to neuronal dysfunction and degeneration. In addition, we demonstrate that LB formation involves a complex interplay between α-syn fibrillization, posttranslational modifications, and interactions between α-syn aggregates and membranous organelles, including mitochondria, the autophagosome, and endolysosome. Finally, we show that the process of LB formation, rather than simply fibril formation, is one of the major drivers of neurodegeneration through disruption of cellular functions and inducing mitochondria damage and deficits, and synaptic dysfunctions. We believe that this model represents a powerful platform to further investigate the mechanisms of LB formation and clearance and to screen and evaluate therapeutics targeting α-syn aggregation and LB formation.

The process of Lewy body formation, rather than simply α-synuclein fibrillization, is one of the major drivers of neurodegeneration

Although converging evidence point to α-synuclein aggregation and Lewy body (LB) formation as central events in Parkinson’s disease, the molecular mechanisms that regulate these processes and their role in disease pathogenesis remain elusive. Herein, we describe a neuronal model that reproduces the key events leading to the formation of inclusions that recapitulate the biochemical, structural, and organizational features of bona fide LBs. This model allowed us to dissect the molecular events associated with the different stages of LB formation and how they contribute to neuronal dysfunctions and degeneration, thus providing a powerful platform for evaluating therapeutics targeting α-synuclein aggregation and LB formation and to identify and validate therapeutic targets for the treatment of Parkinson’s disease.

Parkinson’s disease (PD) is characterized by the accumulation of misfolded and aggregated α-synuclein (α-syn) into intraneuronal inclusions named Lewy bodies (LBs). Although it is widely believed that α-syn plays a central role in the pathogenesis of PD, the processes that govern α-syn fibrillization and LB formation remain poorly understood. In this work, we sought to dissect the spatiotemporal events involved in the biogenesis of the LBs at the genetic, molecular, biochemical, structural, and cellular levels. Toward this goal, we further developed a seeding-based model of α-syn fibrillization to generate a neuronal model that reproduces the key events leading to LB formation, including seeding, fibrillization, and the formation of inclusions that recapitulate many of the biochemical, structural, and organizational features of bona fide LBs. Using an integrative omics, biochemical and imaging approach, we dissected the molecular events associated with the different stages of LB formation and their contribution to neuronal dysfunction and degeneration. In addition, we demonstrate that LB formation involves a complex interplay between α-syn fibrillization, posttranslational modifications, and interactions between α-syn aggregates and membranous organelles, including mitochondria, the autophagosome, and endolysosome. Finally, we show that the process of LB formation, rather than simply fibril formation, is one of the major drivers of neurodegeneration through disruption of cellular functions and inducing mitochondria damage and deficits, and synaptic dysfunctions. We believe that this model represents a powerful platform to further investigate the mechanisms of LB formation and clearance and to screen and evaluate therapeutics targeting α-syn aggregation and LB formation.

Rasagiline and selegiline modulate mitochondrial homeostasis, intervene apoptosis system and mitigate α-synuclein cytotoxicity in disease-modifying therapy for Parkinson's disease

Parkinson's disease has been considered as a motor neuron disease with dopamine (DA) deficit caused by neuronal loss in the substantia nigra, but now proposed as a multi-system disorder associated with α-synuclein accumulation in neuronal and non-neuronal systems. Neuroprotection in Parkinson's disease has intended to halt or reverse cell death of nigro-striatal DA neurons and prevent the disease progression, but clinical studies have not presented enough beneficial results, except the trial of rasagiline by delayed start design at low dose of 1 mg/day only. Now strategy of disease-modifying therapy should be reconsidered taking consideration of accumulation and toxicity of α-synuclein preceding the manifest of motor symptoms. Hitherto neuroprotective therapy has been aimed to mitigate non-specific risk factors; oxidative stress, mitochondrial dysfunction, apoptosis, deficits of neurotrophic factors (NTFs), inflammation and accumulation of pathogenic protein. Future disease-modify therapy should target more specified pathogenic factors, including deregulated mitochondrial homeostasis, deficit of NTFs and α-synuclein toxicity. Selegiline and rasagiline, inhibitors of type B monoamine oxidase, have been proved to exhibit potent neuroprotective function: regulation of mitochondrial apoptosis system, maintenance of mitochondrial function, increased expression of genes coding antioxidant enzymes, anti-apoptotic Bcl-2 and pro-survival NTFs, and suppression of oligomerization and aggregation of α-synuclein and the toxicity in cellular and animal experiments. However, the present available pharmacological therapy starts too late to reverse disease progression, and future disease-modifying therapy should include also non-pharmacological complementary therapy during the prodromal stage.

Mitophagy in Alzheimer's Disease and Other Age-Related Neurodegenerative Diseases

Mitochondrial dysfunction is a central aspect of aging and neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and Huntington's disease. Mitochondria are the main cellular energy powerhouses, supplying most of ATP by oxidative phosphorylation, which is required to fuel essential neuronal functions. Efficient removal of aged and dysfunctional mitochondria through mitophagy, a cargo-selective autophagy, is crucial for mitochondrial maintenance and neuronal health. Mechanistic studies into mitophagy have highlighted an integrated and elaborate cellular network that can regulate mitochondrial turnover. In this review, we provide an updated overview of the recent discoveries and advancements on the mitophagy pathways and discuss the molecular mechanisms underlying mitophagy defects in Alzheimer's disease and other age-related neurodegenerative diseases, as well as the therapeutic potential of mitophagy-enhancing strategies to combat these disorders.

Influence of microcystins-LR (MC-LR) on autophagy in human neuroblastoma SK-N-SH cells

Microcystin-LR (MC-LR) variant exposure poses a potential health hazard to ecosystem, animals, and humans. Previously investigators showed that autophagy plays a key role in MC-LR induced cytotoxicity immortalized murine ovarian granular KK-1 cells and rat Sertoli cells. Recently exposure to MC-LR via drinking water was reported to accumulate in mouse brain with associated adverse oxidant and inflammatory responses. However, autophagy the physiological mechanism required for cells to degrade their own impaired organelles to maintain their homeostasis has not been determined with respect to MC-LR actions on the central nervous system (CNS). Thus, the aim of this study was to examine the effects of MC-LR on autophagy using human neuroblastoma SK-N-SH cells as CNS model. Data demonstrated that after treatment with 15 or 30 µmol/L MC-LR for 48 hr significantly reduced survival rate was noted in SK-N-SH cells. MC-LR increased the expression levels of autophagy-related proteins light chain 3 (LC3) II/I and p62 in SK-N-SH cells, resulting in the accumulation of LC3 and increased intracellular free calcium ion levels. Data indicated that MC-LR induced adverse effects on the CNS as evidenced by decreased cellular survival associated with inhibition of autophagy flux and consequent enhanced autophagosomes accumulation.

Interrogating Parkinson's disease associated redox targets: Potential application of CRISPR editing

Loss of dopaminergic neurons in the substantia nigra is one of the pathogenic hallmarks of Parkinson's disease, yet the underlying molecular mechanisms remain enigmatic. While aberrant redox metabolism strongly associated with iron dysregulation and accumulation of dysfunctional mitochondria is considered as one of the major contributors to neurodegeneration and death of dopaminergic cells, the specific anomalies in the molecular machinery and pathways leading to the PD development and progression have not been identified. The high efficiency and relative simplicity of a new genome editing tool, CRISPR/Cas9, make its applications attractive for deciphering molecular changes driving PD-related impairments of redox metabolism and lipid peroxidation in relation to mishandling of iron, aggregation and oligomerization of alpha-synuclein and mitochondrial injury as well as in mechanisms of mitophagy and programs of regulated cell death (apoptosis and ferroptosis). These insights into the mechanisms of PD pathology may be used for the identification of new targets for therapeutic interventions and innovative approaches to genome editing, including CRISPR/Cas9.

Salidroside Protects Dopaminergic Neurons by Enhancing PINK1/Parkin-Mediated Mitophagy

Parkinson's disease (PD) is a common neurodegenerative disease characterized by the degeneration of nigrostriatal dopaminergic (DA) neurons. Our previous studies have suggested that salidroside (Sal) might play neuroprotective effects against PD by preserving mitochondrial Complex I activity. However, the exact mechanism of the neuroprotective effect of Sal remains unclear. Growing evidence indicates that PINK1/Parkin-mediated mitophagy is involved in the development of PD. In this study, we investigated whether Sal exerts a neuroprotective effect by modulating PINK1/Parkin-mediated mitophagy. Results showed that Sal alleviated MPTP-induced motor deficits in pole test. Moreover, Sal diminished MPTP-induced degeneration of nigrostriatal DA neurons as evidenced by upregulated TH-positive neurons in the substantia nigra, increased DAT expression, and high dopamine and metabolite levels in the striatum. Furthermore, in comparison with the MPP+/MPTP group, Sal considerably increased the mitophagosome and mitophagy flux. Moreover, in comparison with the MPP+/MPTP group, Sal evidently enhanced the mitochondrial expression of PINK1 and Parkin, accompanied by an increase in the colocalization of mitochondria with Parkin. However, transfection of MN9D cells with PINK1 siRNA reversed Sal-induced activated mitophagy and cytoprotective effect. In conclusion, Sal may confer neuroprotective effects by enhancing PINK1/Parkin-mediated mitophagy in MPP+/MPTP-induced PD models.

AAV-Mediated Expression of Dominant-Negative ULK1 Increases Neuronal Survival and Enhances Motor Performance in the MPTP Mouse Model of Parkinson's Disease

Loss of nigrostriatal projections by axonal degeneration is a key early event in Parkinson's disease (PD) pathophysiology, being accountable for the lack of dopamine in the nigrostriatal system and resulting in motor symptoms such as bradykinesia, rigidity, and tremor. Since autophagy is an important mechanism contributing to axonal degeneration, we aimed to evaluate the effects of competitive autophagy inhibition in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD in vivo. Adeno-associated viral vector (AAV)-mediated overexpression of a dominant-negative form of the unc-51 like autophagy-initiating kinase (ULK1.DN) in the substantia nigra was induced 3 weeks before MPTP treatment. Analysis of motor behavior demonstrated a significant improvement of ULK1.DN expressing mice after MPTP treatment. Immunohistochemical analyses of dopaminergic nigral neurons and nigrostriatal projections revealed a significant protection from MPTP-induced neurotoxicity after ULK1.DN expression. Western blot analysis linked these findings to an activation of mTOR signaling. Taken together, our results indicate that expression of ULK1.DN can attenuate MPTP-induced axonal neurodegeneration, suggesting that ULK1 could be a promising novel target in the treatment of PD.

Mitophagy in Parkinson's Disease: From Pathogenesis to Treatment

Parkinson’s disease (PD) is the second most common neurodegenerative disease. The pathogenesis of PD is complicated and remains obscure, but growing evidence suggests the involvement of mitochondrial and lysosomal dysfunction. Mitophagy, the process of removing damaged mitochondria, is compromised in PD patients and models, and was found to be associated with accelerated neurodegeneration. Several PD-related proteins are known to participate in the regulation of mitophagy, including PINK1 and Parkin. In addition, mutations in several PD-related genes are known to cause mitochondrial defects and neurotoxicity by disturbing mitophagy, indicating that mitophagy is a critical component of PD pathogenesis. Therefore, it is crucial to understand how these genes are involved in mitochondrial quality control or mitophagy regulation in the study of PD pathogenesis and the development of novel treatment strategies. In this review, we will discuss the critical roles of mitophagy in PD pathogenesis, highlighting the potential therapeutic implications of mitophagy regulation.

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.

Exploring the "Multiple-Hit Hypothesis" of Neurodegenerative Disease: Bacterial Infection Comes Up to Bat

Despite major strides in personalized genomics, it remains poorly understood why neurodegenerative diseases occur in only a fraction of individuals with a genetic predisposition and conversely, why individuals with no genetic risk of a disorder develop one. Chronic diseases like Alzheimer's, Parkinson's, and Multiple sclerosis are speculated to result from a combination of genetic and environmental factors, a concept commonly referred to as the “multiple hit hypothesis.” A number of bacterial infections have been linked to increased risk of neurodegeneration, and in some cases, clearance of bacterial pathogens has been correlated with amelioration of central nervous system (CNS) deficits. Additionally, mutations in several genes known to contribute to CNS disorders like Parkinson's Disease have repeatedly been implicated in susceptibility to intracellular bacterial infection. Recent data has begun to demonstrate roles for these genes (PARK2, PINK1, and LRRK2) in modulating innate immune outcomes, suggesting that immune dysregulation may play an even more important role in neurodegeneration than previously appreciated. This review will broadly explore the connections between bacterial infection, immune dysregulation, and CNS disorders. Understanding this interplay and how bacterial pathogenesis contributes to the “multiple-hit hypothesis” of neurodegeneration will be crucial to develop therapeutics to effectively treat both neurodegeneration and infection.

Dual Role of Autophagy in Diseases of the Central Nervous System

Autophagy is a vital lysosomal degradation and recycling pathway in the eukaryotic cell, responsible for maintaining an intricate balance between cell survival and cell death, necessary for neuronal survival and function. This dual role played by autophagy raises the question whether this process is a protective or a destructive pathway, the contributor of neuronal cell death or a failed attempt to repair aberrant processes? Deregulated autophagy at different steps of the pathway, whether excessive or downregulated, has been proposed to be associated with neurodegenerative disorders such as Alzheimer's-, Huntington's-, and Parkinson's-disease, known for their intracellular accumulation of protein aggregates. Recent observations of impaired autophagy also appeared in psychiatric disorders such as schizophrenia and bipolar disorder suggesting an additional contribution to the pathophysiology of mental illness. Here we review the current understanding of autophagy's role in various neuropsychiatric disorders and, hitherto, the prevailing new potential autophagy-related therapeutic strategies for their treatment.

Brain mitochondrial proteome alteration driven by creatine deficiency suggests novel therapeutic venues for creatine deficiency syndromes

Creatine (Cr) is a small metabolite with a central role in energy metabolism and mitochondrial function. Creatine deficiency syndromes are inborn errors of Cr metabolism causing Cr depletion in all body tissues and particularly in the nervous system. Patient symptoms involve intellectual disability, language and behavioral disturbances, seizures and movement disorders suggesting that brain cells are particularly sensitive to Cr depletion. Cr deficiency was found to affect metabolic activity and structural abnormalities of mitochondrial organelles; however a detailed analysis of molecular mechanisms linking Cr deficit, energy metabolism alterations and brain dysfunction is still missing. Using a proteomic approach we evaluated the proteome changes of the brain mitochondrial fraction induced by the deletion of the Cr transporter (CrT) in developing mutant mice. We found a marked alteration of the mitochondrial proteomic landscape in the brain of CrT deficient mice, with the overexpression of many proteins involved in energy metabolism and response to oxidative stress. Moreover, our data suggest possible abnormalities of dendritic spines, synaptic function and plasticity, network excitability and neuroinflammatory response. Intriguingly, the alterations occurred in coincidence with the developmental onset of neurological symptoms. Thus, cerebral mitochondrial alterations could represent an early response to Cr deficiency that could be targeted for therapeutic intervention.

Understanding the importance of autophagy in human diseases using Drosophila

Autophagy is a lysosome-dependent intracellular degradation pathway that has been implicated in the pathogenesis of various human diseases, either positively or negatively impacting disease outcomes depending on the specific context. The majority of medical conditions including cancer, neurodegenerative diseases, infections and immune system disorders and inflammatory bowel disease could probably benefit from therapeutic modulation of the autophagy machinery. Drosophila represents an excellent model animal to study disease mechanisms thanks to its sophisticated genetic toolkit, and the conservation of human disease genes and autophagic processes. Here, we provide an overview of the various autophagy pathways observed both in flies and human cells (macroautophagy, microautophagy and chaperone-mediated autophagy), and discuss Drosophila models of the above-mentioned diseases where fly research has already helped to understand how defects in autophagy genes and pathways contribute to the relevant pathomechanisms.

Role of Mitogen Activated Protein Kinase Signaling in Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative disorder caused by insufficient dopamine production due to the loss of 50% to 70% of dopaminergic neurons. A shortage of dopamine, which is predominantly produced by the dopaminergic neurons within the substantia nigra, causes clinical symptoms such as reduction of muscle mass, impaired body balance, akinesia, bradykinesia, tremors, postural instability, etc. Lastly, this can lead to a total loss of physical movement and death. Since no cure for PD has been developed up to now, researchers using cell cultures and animal models focus their work on searching for potential therapeutic targets in order to develop effective treatments. In recent years, genetic studies have prominently advocated for the role of improper protein phosphorylation caused by a dysfunction in kinases and/or phosphatases as an important player in progression and pathogenesis of PD. Thus, in this review, we focus on the role of selected MAP kinases such as JNKs, ERK1/2, and p38 MAP kinases in PD pathology.

Unveiling the olfactory proteostatic disarrangement in Parkinson's disease by proteome-wide profiling

Olfactory dysfunction is one of the earliest features in Lewy-type alpha-synucleinopathies (LTSs) such as Parkinson's disease (PD). However, the underlying molecular mechanisms associated to smell impairment are poorly understood. Applying mass spectrometry-based quantitative proteomics in postmortem olfactory bulbs across limbic, early-neocortical, and neocortical LTS stages of parkinsonian patients, a proteostasis impairment, was observed, identifying 268 differentially expressed proteins between controls and PD phenotypes. In addition, network-driven proteomics revealed a modulation in ERK1/2, MKK3/6, and PDK1/PKC signaling axes. Moreover, a cross-disease study of selected olfactory molecules in sporadic Alzheimer's disease (AD) cases revealed different protein derangements in the modulation of secretagogin (SCGN), calcyclin-binding protein (CACYBP), and glucosamine 6 phosphate isomerase 2 (GNPDA2) between PD and AD. An inverse correlation between GNPDA2 and α-synuclein protein levels was also reflected in PD cerebrospinal fluid. Interestingly, PD patients exhibited significantly lower serum GNPDA2 levels than controls (n = 82/group). Our study provides important avenues for understanding the olfactory bulb proteostasis imbalance in PD, deciphering mechanistic clues to the equivalent smell deficits observed in AD and PD pathologies.

Induction of the Immunoproteasome Subunit Lmp7 Links Proteostasis and Immunity in α-Synuclein Aggregation Disorders

Accumulation of aggregated α-synuclein into Lewy bodies is thought to contribute to the onset and progression of dopaminergic neuron degeneration in Parkinson's disease (PD) and related disorders. Although protein aggregation is associated with perturbation of proteostasis, how α-synuclein aggregation affects the brain proteome and signaling remains uncertain. In a mouse model of α-synuclein aggregation, 6% of 6215 proteins and 1.6% of 8183 phosphopeptides changed in abundance, indicating conservation of proteostasis and phosphorylation signaling. The proteomic analysis confirmed changes in abundance of proteins that regulate dopamine synthesis and transport, synaptic activity and integrity, and unearthed changes in mRNA binding, processing and protein translation. Phosphorylation signaling changes centered on axonal and synaptic cytoskeletal organization and structural integrity. Proteostatic responses included a significant increase in the levels of Lmp7, a component of the immunoproteasome. Increased Lmp7 levels and activity were also quantified in postmortem human brains with PD and dementia with Lewy bodies. Functionally, the immunoproteasome degrades α-synuclein aggregates and generates potentially antigenic peptides. Expression and activity of the immunoproteasome may represent testable targets to induce adaptive responses that maintain proteome integrity and modulate immune responses in protein aggregation disorders.

Age- and disease-dependent increase of the mitophagy marker phospho-ubiquitin in normal aging and Lewy body disease

Although exact causes of Parkinson disease (PD) remain enigmatic, mitochondrial dysfunction is increasingly appreciated as a key determinant of dopaminergic neuron susceptibility in both familial and sporadic PD. Two genes associated with recessive, early-onset PD encode the ubiquitin (Ub) kinase PINK1 and the E3 Ub ligase PRKN/PARK2/Parkin, which together orchestrate a protective mitochondrial quality control (mitoQC) pathway. Upon stress, both enzymes cooperatively identify and decorate damaged mitochondria with phosphorylated poly-Ub (p-S65-Ub) chains. This specific label is subsequently recognized by autophagy receptors that further facilitate mitochondrial degradation in lysosomes (mitophagy). Here, we analyzed human post-mortem brain specimens and identified distinct pools of p-S65-Ub-positive structures that partially colocalized with markers of mitochondria, autophagy, lysosomes and/or granulovacuolar degeneration bodies. We further quantified levels and distribution of the ‘mitophagy tag’ in 2 large cohorts of brain samples from normal aging and Lewy body disease (LBD) cases using unbiased digital pathology. Somatic p-S65-Ub structures independently increased with age and disease in distinct brain regions and enhanced levels in LBD brain were age- and Braak tangle stage-dependent. Additionally, we observed significant correlations of p-S65-Ub with LBs and neurofibrillary tangle levels in disease. The degree of co-existing p-S65-Ub signals and pathological PD hallmarks increased in the pre-mature stage, but decreased in the late stage of LB or tangle aggregation. Altogether, our study provides further evidence for a potential pathogenic overlap among different forms of PD and suggests that p-S65-Ub can serve as a biomarker for mitochondrial damage in aging and disease.

Abbreviations: BLBD: brainstem predominant Lewy body disease; CCCP: carbonyl cyanide m-chlorophenyl hydrazone; DLB: dementia with Lewy bodies; DLBD: diffuse neocortical Lewy body disease; EOPD: early-onset Parkinson disease; GVB: granulovacuolar degeneration body; LB: Lewy body; LBD: Lewy body disease; mitoQC: mitochondrial quality control; nbM: nucleus basalis of Meynert; PD: Parkinson disease; PDD: Parkinson disease with dementia; p-S65-Ub: PINK1-phosphorylated serine 65 ubiquitin; SN: substantia nigra; TLBD: transitional Lewy body disease; Ub: ubiquitin

Mechanisms of selective autophagy and mitophagy: Implications for neurodegenerative diseases

Over the past 20 years, the concept of mammalian autophagy as a nonselective degradation system has been repudiated, due in part to important discoveries in neurodegenerative diseases, which opened the field of selective autophagy. Protein aggregates and damaged mitochondria represent key pathological hallmarks shared by most neurodegenerative diseases. The landmark discovery in 2007 of p62/SQSTM1 as the first mammalian selective autophagy receptor defined a new family of autophagy-related proteins that serve to target protein aggregates, mitochondria, intracellular pathogens and other cargoes to the core autophagy machinery via an LC3-interacting region (LIR)-motif. Notably, mutations in the LIR-motif proteins p62 (SQSTM1) and optineurin (OPTN) contribute to familial forms of frontotemporal dementia and amyotrophic lateral sclerosis. Moreover, a subset of LIR-motif proteins is involved in selective mitochondrial degradation initiated by two recessive familial Parkinson's disease genes. PTEN-induced kinase 1 (PINK1) activates the E3 ubiquitin ligase Parkin (PARK2) to mark depolarized mitochondria for degradation. An extensive body of literature delineates key mechanisms in this pathway, based mostly on work in transformed cell lines. However, the potential role of PINK1-triggered mitophagy in neurodegeneration remains a conundrum, particularly in light of recent in vivo mitophagy studies. There are at least three major mechanisms by which mitochondria are targeted for mitophagy: transmembrane receptor-mediated, ubiquitin-mediated and cardiolipin-mediated. This review summarizes key features of the major cargo recognition pathways for selective autophagy and mitophagy, highlighting their potential impact in the pathogenesis or amelioration of neurodegenerative diseases.

A new outlook on cholinergic interneurons in Parkinson's disease and L-DOPA-induced dyskinesia

Traditionally, dopamine (DA) and acetylcholine (ACh) striatal systems were considered antagonistic and imbalances or aberrant signaling between these neurotransmitter systems could be detrimental to basal ganglia activity and pursuant motor function, such as in Parkinson's disease (PD) and L-DOPA-induced dyskinesia (LID). Herein, we discuss the involvement of cholinergic interneurons (ChIs) in striatally-mediated movement in a healthy, parkinsonian, and dyskinetic state. ChIs integrate numerous neurotransmitter signals using intrinsic glutamate, serotonin, and DA receptors and convey the appropriate transmission onto nearby muscarinic and nicotinic ACh receptors to produce movement. In PD, severe DA depletion causes abnormal rises in ChI activity which promote striatal signaling to attenuate normal movement. When treating PD with L-DOPA, hyperkinetic side effects, or LID, develop due to increased striatal DA; however, the role of ChIs and ACh transmission, until recently has been unclear. Fortunately, new technology and pharmacological agents have facilitated understanding of ChI function and ACh signaling in the context of LID, thus offering new opportunities to modify existing and discover future therapeutic strategies in movement disorders.

Autophagy Disruptions Associated With Altered Optineurin Expression in Extranigral Regions in a Rotenone Model of Parkinson's Disease

The motor features of Parkinson's disease (PD) primarily result from a lesion to the nigrostriatal dopamine system. Numerous non-motor symptoms occur in PD, many of which are postulated to stem from pathology outside of the nigrostriatal dopamine system. Perturbations to protein trafficking, disruption of mitochondrial integrity, and impaired autophagy have repeatedly been implicated in dopaminergic neuron cell death. Previously, we demonstrated that multiple markers of autophagy are disrupted in a rotenone model of PD, with alterations occurring prior to an overt lesion to the nigrostriatal dopamine system. Whether these events occur in extra-nigral nuclei in PD and when relative to a lesion in the nigrostriatal dopamine system are generally unknown. The primary goal of these studies was to determine whether autophagy disruptions, in non-dopaminergic neuronal populations occur in an environmental model of PD utilizing a mitochondrial toxin. Here, we utilized the rat rotenone PD model, with sampling time-points before and after an overt lesion to the nigrostriatal dopamine system. In analyzing autophagy changes, we focused on optineurin (OPTN) and the autophagy marker, LC3. OPTN is an autophagy cargo adapter protein genetically linked to amyotrophic lateral sclerosis and glaucoma. In the present study, we observed OPTN enrichment in all PD-relevant brain regions examined. Further, alterations in OPTN and LC3 expression and colocalized puncta suggest specific impairments to autophagy that will inform future mechanistic studies. Thus, our data suggest that autophagy disruptions may be critical to PD pathogenesis in non-dopaminergic neurons and the onset of non-motor symptoms.

Multiple pathways for mitophagy: A neurodegenerative conundrum for Parkinson's disease

It has been nearly a decade since the first landmark studies implicating familial recessive Parkinson's disease genes in the regulation of selective mitochondrial autophagy. The PTEN-induced kinase 1 (PINK1) and the E3 ubiquitin ligase Parkin (encoded by the PARK2 gene) act together to mark depolarized mitochondria for degradation. There is now an extensive body of literature detailing key mediators and steps in this pathway, based mostly on work in transformed cell lines. However, the degree to which PINK1-triggered mitophagy contributes to mitochondrial quality control in the mammalian brain, and the extent to which its disruption contributes to Parkinson's disease pathogenesis remain uncertain. In recent years, it has become clear that there are multiple, potentially redundant, pathways of cargo specification for mitophagy. Important mitophagy-independent functions of PINK1 and Parkin are also emerging. This review summarizes key features of three major mitophagy cargo recognition systems: receptor-mediated, ubiquitin-mediated and cardiolipin-mediated. New animal models that may be useful for tracking the delivery of mitochondria into lysosomes in different neuronal populations will be highlighted. Combining these research tools with methods to selectively disrupt specific mitophagy pathways may lead to a better understanding of the potential role of mitophagy in modulating neuronal vulnerability in Parkinson's spectrum (PD/PDD/DLB) and other neurodegenerative diseases.

The mitochondrial transcription factor TFAM in neurodegeneration: emerging evidence and mechanisms

The mitochondrial transcription factor A, or TFAM, is a mitochondrial DNA (mtDNA)-binding protein essential for genome maintenance. TFAM functions in determining the abundance of the mitochondrial genome by regulating packaging, stability, and replication. More recently, TFAM has been shown to play a central role in the mtDNA stress-mediated inflammatory response. Emerging evidence indicates that decreased mtDNA copy number is associated with several aging-related pathologies; however, little is known about the association of TFAM abundance and disease. In this Review, we evaluate the potential associations of altered TFAM levels or mtDNA copy number with neurodegeneration. We also describe potential mechanisms by which mtDNA replication, transcription initiation, and TFAM-mediated endogenous danger signals may impact mitochondrial homeostasis in Alzheimer, Huntington, Parkinson, and other neurodegenerative diseases.

The lysosomal enzyme alpha-Galactosidase A is deficient in Parkinson's disease brain in association with the pathologic accumulation of alpha-synuclein

The aberrant accumulation of alpha-synuclein (α-syn) is believed to contribute to the onset and pathogenesis of Parkinson's disease (PD). The autophagy-lysosome pathway (ALP) is responsible for the high capacity clearance of α-syn. ALP dysfunction is documented in PD and pre-clinical evidence suggests that inhibiting the ALP promotes the pathological accumulation of α-syn. We previously identified the pathological accumulation of α-syn in the brains of mice deficient for the soluble lysosomal enzyme alpha-Galactosidase A (α-Gal A), a member of the glycosphingolipid metabolism pathway. In the present study, we quantified α-Gal A activity and levels of its glycosphingolipid metabolites in postmortem temporal cortex specimens from control individuals and in PD individuals staged with respect to α-syn containing Lewy body pathology. In late-state PD temporal cortex we observed significant decreases in α-Gal A activity and the 46kDa "active" species of α-Gal A as determined respectively by fluorometric activity assay and western blot analysis. These decreases in α-Gal A activity/levels correlated significantly with increased α-syn phosphorylated at serine 129 (p129S-α-syn) that was maximal in late-stage PD temporal cortex. Mass spectrometric analysis of 29 different isoforms of globotriaosylceramide (Gb3), a substrate of α-Gal A indicated no significant differences with respect to different stages of PD temporal cortex. However, significant correlations were observed between increased levels of several Gb3 isoforms and with decreased α-Gal A activity and/or increased p129S-α-syn. Deacylated Gb3 (globotriaosylsphingosine or lyso-Gb3) was also analyzed in PD brain tissue but was below the limit of detection of 20pmol/g. Analysis of other lysosomal enzymes revealed a significant decrease in activity for the lysosomal aspartic acid protease cathepsin D but not for glucocerebrosidase (GCase) or cathepsin B in late-stage PD temporal cortex. However, a significant correlation was observed between decreasing GCase activity and increasing p129S-α-syn. Together our findings indicate α-Gal A deficiency in late-stage PD brain that correlates significantly with the pathological accumulation of α-syn, and further suggest the potential for α-Gal A and its glycosphingolipid substrates as putative biomarkers for PD.

Parkinson's disease: experimental models and reality

Parkinson's disease (PD) is a chronic, progressive movement disorder of adults and the second most common neurodegenerative disease after Alzheimer's disease. Neuropathologic diagnosis of PD requires moderate-to-marked neuronal loss in the ventrolateral substantia nigra pars compacta and α-synuclein (αS) Lewy body pathology. Nigrostriatal dopaminergic neurodegeneration correlates with the Parkinsonian motor features, but involvement of other peripheral and central nervous system regions leads to a wide range of non-motor features. Nigrostriatal dopaminergic neurodegeneration is shared with other parkinsonian disorders, including some genetic forms of parkinsonism, but many of these disorders do not have Lewy bodies. An ideal animal model for PD, therefore, should exhibit age-dependent and progressive dopaminergic neurodegeneration, motor dysfunction, and abnormal αS pathology. Rodent models of PD using genetic or toxin based strategies have been widely used in the past several decades to investigate the pathogenesis and therapeutics of PD, but few recapitulate all the major clinical and pathologic features of PD. It is likely that new strategies or better understanding of fundamental disease processes may facilitate development of better animal models. In this review, we highlight progress in generating rodent models of PD based on impairments of four major cellular functions: mitochondrial oxidative phosphorylation, autophagy-lysosomal metabolism, ubiquitin-proteasome protein degradation, and endoplasmic reticulum stress/unfolded protein response. We attempt to evaluate how impairment of these major cellular systems contribute to PD and how they can be exploited in rodent models. In addition, we review recent cell biological studies suggesting a link between αS aggregation and impairment of nuclear membrane integrity, as observed during cellular models of apoptosis. We also briefly discuss the role of incompetent phagocytic clearance and how this may be a factor to consider in developing new rodent models of PD.

Absence of Neurofibromin Induces an Oncogenic Metabolic Switch via Mitochondrial ERK-Mediated Phosphorylation of the Chaperone TRAP1

Mutations in neurofibromin, a Ras GTPase-activating protein, lead to the tumor predisposition syndrome neurofibromatosis type 1. Here, we report that cells lacking neurofibromin exhibit enhanced glycolysis and decreased respiration in a Ras/ERK-dependent way. In the mitochondrial matrix of neurofibromin-deficient cells, a fraction of active ERK1/2 associates with succinate dehydrogenase (SDH) and TRAP1, a chaperone that promotes the accumulation of the oncometabolite succinate by inhibiting SDH. ERK1/2 enhances both formation of this multimeric complex and SDH inhibition. ERK1/2 kinase activity is favored by the interaction with TRAP1, and TRAP1 is, in turn, phosphorylated in an ERK1/2-dependent way. TRAP1 silencing or mutagenesis at the serine residues targeted by ERK1/2 abrogates tumorigenicity, a phenotype that is reverted by addition of a cell-permeable succinate analog. Our findings reveal that Ras/ERK signaling controls the metabolic changes orchestrated by TRAP1 that have a key role in tumor growth and are a promising target for anti-neoplastic strategies.

Mitochondrial Calcium Dysregulation Contributes to Dendrite Degeneration Mediated by PD/LBD-Associated LRRK2 Mutants

Mutations in leucine-rich repeat kinase 2 (LRRK2) contribute to development of late-onset familial Parkinson's disease (PD), with clinical features of motor and cognitive dysfunction indistinguishable from sporadic PD. Calcium dysregulation plays an important role in PD pathogenesis, but the mechanisms of neurodegeneration remain unclear. Recent reports indicate enhanced excitatory neurotransmission in cortical neurons expressing mutant LRRK2, which occurs before the well-characterized phenotype of dendritic shortening. As mitochondria play a major role in the rapid buffering of cytosolic calcium, we hypothesized that altered mitochondrial calcium handling contributes to dendritic retraction elicited by the LRRK2-G2019S and -R1441C mutations. In primary mouse cortical neurons, we observed increased depolarization-induced mitochondrial calcium uptake. We found that expression of mutant LRRK2 elicited transcriptional upregulation of the mitochondrial calcium uniporter (MCU) and the mitochondrial calcium uptake 1 protein (MICU1) with no change in levels of the mitochondrial calcium antiporter NCLX. Elevated MCU and MICU1 were also observed in LRRK2-mutated patient fibroblasts, along with increased mitochondrial calcium uptake, and in postmortem brains of sporadic PD/PDD patients of both sexes. Transcriptional upregulation of MCU and MICU1 was caused by activation of the ERK1/2 (MAPK3/1) pathway. Inhibiting ERK1/2 conferred protection against mutant LRRK2-induced neurite shortening. Pharmacological inhibitors or RNAi knockdown of MCU attenuated mitochondrial calcium uptake and dendritic/neuritic shortening elicited by mutant LRRK2, whereas expression of a constitutively active mutant of NCLX that enhances calcium export from mitochondria was neuroprotective. These data suggest that an increased susceptibility to mitochondrial calcium dysregulation contributes to dendritic injury in mutant LRRK2 pathogenesis.SIGNIFICANCE STATEMENT Cognitive dysfunction and dementia are common features of Parkinson's disease (PD), causing significant disability. Mutations in LRRK2 represent the most common known genetic cause of PD. We found that PD-linked LRRK2 mutations increased dendritic and mitochondrial calcium uptake in cortical neurons and familial PD patient fibroblasts, accompanied by increased expression of the mitochondrial calcium transporter MCU. Blocking the ERK1/2-dependent upregulation of MCU conferred protection against mutant LRRK2-elicited dendrite shortening, as did inhibiting MCU-mediated calcium import. Conversely, stimulating the export of calcium from mitochondria was also neuroprotective. These results implicate increased susceptibility to mitochondrial calcium overload in LRRK2-driven neurodegeneration, and suggest possible interventions that may slow the progression of cognitive dysfunction in PD.

Neuroprotective Effects of Loganin on MPTP-Induced Parkinson's Disease Mice: Neurochemistry, Glial Reaction and Autophagy Studies

Parkinson's disease (PD) is a progressive neurodegenerative disease, involving resting tremor and bradykinesia, for which no recognized therapies or drugs are available to halt or slow progression. In recent years, natural botanic products have been considered relatively safe, with limited side effects, and are expected to become an important source for clinical mediation of PD in the future. Our study focuses on the ability of loganin, a compound derived from fruits of cornus, to mediate neuroprotection in a mouse model of PD. Mice were administered 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) with a dosage of 30 mg/kg daily for 5 days to establish a subacute PD model and treated with loganin. Locomotor activity was assessed by a pole test, then mice were euthanized at 1 and 3 days after the last treatment, and brain tissue was prepared for subsequent assays. Loganin rescued decrease of dopamine levels and tyrosine hydroxylase (TH) expression in the striatum, and shortened total locomotor activity (TLA) time of mice. Furthermore, loganin alleviated microglia and astrocyte activation, and suppressed TNF-α and caspase-3 expression through a c-Abl-p38-NFκB pathway. Loganin also downregulated LC3-II and Drp1 expression, and decreased the level of acidic vesicular organelles (AVOs). Loganin exerts neuroprotective effects on MPTP-induced PD mice by decreasing inflammation, autophagy, and apoptosis, suggesting that loganin could serve as a therapeutic drug to ameliorate PD. J. Cell. Biochem. 118: 3495-3510, 2017. © 2017 Wiley Periodicals, Inc.

Subcellular Fractionation for ERK Activation Upon Mitochondrial-derived Peptide Treatment

Mitochondrial-derived peptides (MDPs) are a new class of peptides that are encoded by small open reading frames within other known genes of the mitochondrial genome. MDPs have a wide variety of biological effects such as protecting neurons from apoptosis, improving metabolic markers, and protecting cells from chemotherapy. Humanin was the first MDP to be discovered and is the most studied peptide among the MDP family. The membrane receptors and downstream signaling pathways of humanin have been carefully characterized. Additional MDPs such as MOTS-c and SHLP1-6 have been more recently discovered and the signaling mechanisms have yet to be elucidated. Here we describe a cell culture based method to determine the function of these peptides. In particular, cell fractionation techniques in combination with western blotting allow for the quantitative determination of activation and translocation of important signaling molecule. While there are other methods of cell fractionation, the one described here is an easy and straightforward method. These methods can be used to further elucidate the mechanism of action of these peptides and other therapeutic agents.

Cellular models as tools for the study of the role of alpha-synuclein in Parkinson's disease

Neurodegenerative diseases are highly debilitating conditions characterised primarily by progressive neuronal loss and impairment of the nervous system. Parkinson's disease (PD) is one of the most common of these disorders, affecting 1-2% of the population above the age of 65. Although the underlying mechanisms of PD have been extensively studied, we still lack a full understanding of the molecular underpinnings of the disease. Thus, the in vitro and in vivo models currently used are able to only partially recapitulate the typical phenotypes of the disease. Here, we review various cell culture models currently used to study the molecular basis of PD, with a focus on alpha-synuclein-associated molecular pathologies. We also discuss how different cell models may constitute powerful tools for high-throughput screening of molecules capable of modulating alpha-synuclein toxicity.

Melatonin attenuates MPTP-induced neurotoxicity via preventing CDK5-mediated autophagy and SNCA/α-synuclein aggregation

Autophagy is involved in the pathogenesis of neurodegenerative diseases including Parkinson disease (PD). However, little is known about the regulation of autophagy in neurodegenerative process. In this study, we characterized aberrant activation of autophagy induced by neurotoxin 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP) and demonstrated that melatonin has a protective effect on neurotoxicity. We found an excessive activation of autophagy in monkey brain tissues and C6 cells, induced by MPTP, which is mediated by CDK5 (cyclin-dependent kinase 5). MPTP treatment significantly reduced total dendritic length and dendritic complexity of cultured primary cortical neurons and melatonin could reverse this effect. Decreased TH (tyrosine hydroxylase)-positive cells and dendrites of dopaminergic neurons in the substantia nigra pars compacta (SNc) were observed in MPTP-treated monkeys and mice. Along with decreased TH protein level, we observed an upregulation of CDK5 and enhanced autophagic activity in the striatum of mice with MPTP injection. These changes could be salvaged by melatonin treatment or knockdown of CDK5. Importantly, melatonin or knockdown of CDK5 reduced MPTP-induced SNCA/α-synuclein aggregation in mice, which is widely thought to trigger the pathogenesis of PD. Finally, melatonin or knockdown of CDK5 counteracted the PD phenotype in mice induced by MPTP. Our findings uncover a potent role of CDK5-mediated autophagy in the pathogenesis of PD, and suggest that control of autophagic pathways may provide an important clue for exploring potential target for novel therapeutics of PD.

From the Cover: Alterations in Optineurin Expression and Localization in Pre-clinical Parkinson's Disease Models

Parkinson's disease (PD) is a progressive neurodegenerative disease that affects ∼5 million people around the world. PD etiopathogenesis is poorly understood and curative or disease modifying treatments are not available. Mechanistic studies have identified numerous pathogenic pathways that overlap with many other neurodegenerative diseases. Mutations in the protein optineurin (OPTN) have recently been identified as causative factors for glaucoma and amyotrophic lateral sclerosis. OPTN has multiple recognized roles in neurons, notably in mediating autophagic flux, which has been found to be disrupted in most neurodegenerative diseases. OPTN(+ )aggregates have preliminarily been identified in cytoplasmic inclusions in numerous neurodegenerative diseases, however, whether OPTN has a role in PD pathogenesis has yet to be tested. Thus, we chose to test the hypothesis that OPTN expression and localization would be modulated in pre-clinical PD models. To test our hypothesis, we characterized midbrain OPTN expression in normal rats and in a rat rotenone PD model. For the first time, we show that OPTN is enriched in dopamine neurons in the midbrain, and its expression is modulated by rotenone treatment in vivo Here, animals were sampled at time-points both prior to overt neurodegeneration and after severe behavioral deficits, where a lesion to the nigrostriatal dopamine system is present. The effect and magnitude of OPTN expression changes are dependent on duration of treatment. Furthermore, OPTN colocalizes with LC3 (autophagic vesicle marker) and alpha-synuclein positive puncta in rotenone-treated animals, potentially indicating an important role in autophagy and PD pathogenesis.

The dynamic subcellular localization of ERK: mechanisms of translocation and role in various organelles

The dynamic subcellular localization of ERK in resting and stimulated cells plays an important role in its regulation. In resting cells, ERK localizes in the cytoplasm, and upon stimulation, it translocates to its target substrates and organelles. ERK signaling initiated from different places in resting cells has distinct outcomes. In this review, we summarize the mechanisms of ERK1/2 translocation to the nucleus and mitochondria, and of ERK1c to the Golgi. We also show that ERK1/2 translocation to the nucleus is a useful anti cancer target. Unraveling the complex subcellular localization of ERK and its dynamic changes upon stimulation provides a better understanding of the regulation of ERK signaling and may result in the development of new strategies to combat ERK-related diseases.

Autophagy and Alpha-Synuclein: Relevance to Parkinson's Disease and Related Synucleopathies

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.

Effect of the pituitary adenylate cyclase-activating polypeptide on the autophagic activation observed in in vitro and in vivo models of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder that leads to destruction of the midbrain dopaminergic (DA) neurons. This phenomenon is related to apoptosis and its activation can be blocked by the pituitary adenylate cyclase-activating polypeptide (PACAP). Growing evidence indicates that autophagy, a self-degradation activity that cleans up the cell, is induced during the course of neurodegenerative diseases. However, the role of autophagy in the pathogenesis of neuronal disorders is yet poorly understood and the potential ability of PACAP to modulate the related autophagic activation has never been significantly investigated. Hence, we explored the putative autophagy-modulating properties of PACAP in in vitro and in vivo models of PD, using the neurotoxic agents 1-methyl-4-phenylpyridinium (MPP(+)) and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), respectively, to trigger alterations of DA neurons. In both models, following the toxin exposure, PACAP reduced the autophagic activity as evaluated by the production of LC3 II, the modulation of the p62 protein levels, and the formation of autophagic vacuoles. The ability of PACAP to inhibit autophagy was also observed in an in vitro cell assay by the blocking of the p62-sequestration activity produced with the autophagy inducer rapamycin. Thus, the results demonstrated that autophagy is induced in PD experimental models and that PACAP exhibits not only anti-apoptotic but also anti-autophagic properties.

Extremely low frequency electromagnetic fields affect proliferation and mitochondrial activity of human cancer cell lines

PURPOSE

To date, the effects of electromagnetic fields on cell metabolism have been overlooked. The objective of the present study was to investigate the influence of extremely low frequency electromagnetic fields (ELF-EMF) over mitochondrial metabolism and the consequent impact on cancer cell growth.

MATERIALS AND METHODS

The effects of ELF-EMF on cancer growth were investigated in several human cancer cell lines by crystal violet assay. The modulation of mitochondrial activity was assessed by cytofluorimetric evaluation of membrane potential and by real-time quantification of mitochondrial transcription. Moreover the expression of several mitochondrial proteins and their levels in the organelle were evaluated.

RESULTS

The long-term exposure to ELF-EMF reduced the proliferation of several cancer cell lines and the effect was associated to an increased mitochondrial activity without evident changes in ATP levels. The results of our experiments excluded a transcriptional modulation of mitochondrial respiratory complexes, rather suggesting that ELF-EMF increased the energy demand. The altered mitochondrial metabolism led to changes in mitochondrial protein profile. In fact we found a downregulated expression of mitochondrial phospho-ERK, p53 and cytochrome c.

CONCLUSION

The results of the present study indicate that ELF-EMF can negatively modulate cancer cell growth increasing respiratory activity of cells and altering mitochondrial protein expression.

Parkin represses 6-hydroxydopamine-induced apoptosis via stabilizing scaffold protein p62 in PC12 cells

AIM

Parkin has been shown to exert protective effects against 6-hydroxydopamine (6-OHDA)-induced neurotoxicity in different models of Parkinson disease. In the present study we investigated the molecular mechanisms underlying the neuroprotective action of parkin in vitro.

METHODS

HEK293, HeLa and PC12 cells were transfected with parkin, parkin mutants, p62 or si-p62. Protein expression and ubiquitination were assessed using immunoblot analysis. Immunoprecipitation assay was performed to identify the interaction between parkin and scaffold protein p62. PC12 and SH-SY5Y cells were treated with 6-OHDA (200 μmol/L), and cell apoptosis was detected using PI and Hoechst staining.

RESULTS

In HEK293 cells co-transfected with parkin and p62, parkin was co-immunoprecipitated with p62, and parkin overexpression increased p62 protein levels. In parkin-deficient HeLa cells, transfection with wild-type pakin, but not with ligase activity-deficient pakin mutants, significantly increased p62 levels, suggesting that parkin stabilized p62 through its E3 ligase activity. Transfection with parkin or p62 significantly repressed ERK1/2 phosphorylation in HeLa cells, but transfection with parkin did not repress ERK1/2 phosphorylation in p62-knockdown HeLa cells, suggesting that p62 was involved in parkin-induced inhibition on ERK1/2 phosphorylation. Overexpression of parkin or p62 significantly repressed 6-OHDA-induced ERK1/2 phosphorylation in PC12 cells, and parkin overexpression inhibited 6-OHDA-induced apoptosis in PC12 and SH-SY5Y cells.

CONCLUSION

Parkin protects PC12 cells against 6-OHDA-induced apoptosis via ubiquitinating and stabilizing scaffold protein p62, and repressing ERK1/2 activation.

Inhibition of MEK confers hypersensitivity to X-radiation in the context of BRAF mutation in a model of childhood astrocytoma

PURPOSE

Curative therapy for childhood glioma presents challenges when complete resection is not possible. Patients with recurrent low-grade tumors or anaplastic astrocytoma may receive radiation treatment; however, the long-term sequellae from radiation treatment can be severe. As many childhood gliomas are associated with activation of BRAF, we have explored the combination of ionizing radiation with MEK inhibition in a model of BRAF-mutant anaplastic astrocytoma.

EXPERIMENTAL DESIGN

The regulation of TORC1 signaling by BRAF was examined in BT-40 (BRAF mutant) and BT-35 (BRAF wild type) xenografts, in a cell line derived from the BT-40 xenograft and two adult BRAF mutant glioblastoma cell lines. The effect of MEK inhibition (selumetinib), XRT (total dose 10 Gy as 2 Gy daily fractions), or the combination of selumetinib and XRT was evaluated in subcutaneous BT-40 xenografts.

RESULTS

Inhibition of MEK signaling by selumetinib suppressed TORC1 signaling only in the context of the BRAF-mutant both in vitro and in vivo. Inhibition of MEK signaling in BT-40 cells or in xenografts lead to a complete suppression of FANCD2 and conferred hypersensitivity to XRT in BT-40 xenografts without increasing local skin toxicity.

CONCLUSIONS

Selumetinib suppressed TORC1 signaling in the context of BRAF mutation. Selumetinib caused a rapid downregulation of FANCD2 and markedly potentiated the effect of XRT. These data suggest the possibility of potentiating the effect of XRT selectively in tumor cells by MEK inhibition in the context of mutant BRAF or maintaining tumor control at lower doses of XRT that would decrease long-term sequelae.

The proinflammatory cytokine, interleukin-17A, augments mitochondrial function and neurite outgrowth of cultured adult sensory neurons derived from normal and diabetic rats

BACKGROUND

Diabetic neuropathy comprises dying back of nerve endings that reflects impairment in axonal plasticity and regenerative nerve growth. Metabolic changes in diabetes can lead to a dysregulation of hormonal mediators, such as cytokines, that may constrain distal nerve fiber growth. Interleukin-17 (IL-17A), a proinflammatory and neurotropic cytokine produced by T-cells, was significantly reduced in sciatic nerve of streptozotocin (STZ)-diabetic rats. Thus we studied the effect of IL-17A on the phenotype of sensory neurons derived from age matched control or type 1 diabetic rats. The aims were to determine the ability of IL-17A to enhance neurite outgrowth in cultured sensory neurons, investigate the signaling pathways activated by IL-17A, study the role of mitochondria and mechanistically link to neurite outgrowth.

RESULTS

IL-17A (10 ng/ml; p<0.05) significantly and dose-dependently increased total neurite outgrowth in cultures of adult dorsal root ganglia (DRG) sensory neurons derived from both control and streptozotocin (STZ)-diabetic rats. This enhancement was mediated by IL-17A-dependent activation of extracellular-regulated protein kinase (ERK) and phosphoinositide-3 kinase (PI-3K) signal transduction pathways. Pharmacological blockade of one of these activated pathways triggered complete inhibition of neurite outgrowth. IL-17A augmented mitochondrial bioenergetic function of sensory neurons derived from control or diabetic rats and this was also mediated via ERK or PI-3K. IL-17A-dependent elevation of bioenergetic function was associated with augmented expression of proteins of the mitochondrial electron transport system complexes.

CONCLUSIONS

IL-17A enhanced axonal plasticity through activation of ERK and PI-3K pathways and was associated with augmented mitochondrial bioenergetic function in sensory neurons.

Cdk5 activity in the brain - multiple paths of regulation

Cyclin dependent kinase-5 (Cdk5), a family member of the cyclin-dependent kinases, plays a pivotal role in the central nervous system. During embryogenesis, Cdk5 is indispensable for brain development and, in the adult brain, it is essential for numerous neuronal processes, including higher cognitive functions such as learning and memory formation. However, Cdk5 activity becomes deregulated in several neurological disorders, such as Alzheimer's disease, Parkinson's disease and Huntington's disease, which leads to neurotoxicity. Therefore, precise control over Cdk5 activity is essential for its physiological functions. This Commentary covers the various mechanisms of Cdk5 regulation, including several recently identified protein activators and inhibitors of Cdk5 that control its activity in normal and diseased brains. We also discuss the autoregulatory activity of Cdk5 and its regulation at the transcriptional, post-transcriptional and post-translational levels. We finally highlight physiological and pathological roles of Cdk5 in the brain. Specific modulation of these protein regulators is expected to provide alternative strategies for the development of effective therapeutic interventions that are triggered by deregulation of Cdk5.

Coordinated activation of AMP-activated protein kinase, extracellular signal-regulated kinase, and autophagy regulates phorbol myristate acetate-induced differentiation of SH-SY5Y neuroblastoma cells

We explored the interplay between the intracellular energy sensor AMP-activated protein kinase (AMPK), extracellular signal-regulated kinase (ERK), and autophagy in phorbol myristate acetate (PMA)-induced neuronal differentiation of SH-SY5Y human neuroblastoma cells. PMA-triggered expression of neuronal markers (dopamine transporter, microtubule-associated protein 2, β-tubulin) was associated with an autophagic response, measured by the conversion of microtubule-associated protein light chain 3 (LC3)-I to autophagosome-bound LC3-II, increase in autophagic flux, and expression of autophagy-related (Atg) proteins Atg7 and beclin-1. This coincided with the transient activation of AMPK and sustained activation of ERK. Pharmacological inhibition or RNA interference-mediated silencing of AMPK suppressed PMA-induced expression of neuronal markers, as well as ERK activation and autophagy. A selective pharmacological blockade of ERK prevented PMA-induced neuronal differentiation and autophagy induction without affecting AMPK phosphorylation. Conversely, the inhibition of autophagy downstream of AMPK/ERK, either by pharmacological agents or LC3 knockdown, promoted the expression of neuronal markers, thus indicating a role of autophagy in the suppression of PMA-induced differentiation of SH-SY5Y cells. Therefore, PMA-induced neuronal differentiation of SH-SY5Y cells depends on a complex interplay between AMPK, ERK, and autophagy, in which the stimulatory effects of AMPK/ERK signaling are counteracted by the coinciding autophagic response. Phorbol myristate acetate (PMA) induces the expression of dopamine transporter, microtubule-associated protein 2, and β-tubulin, and subsequent neuronal differentiation of SH-SY5Y neuroblastoma cells through AMP-activated protein kinase (AMPK)-dependent activation of extracellular signal-regulated kinase (ERK). The activation of AMPK/ERK axis also induces the expression of beclin-1 and Atg7, and increases LC3 conversion, thereby triggering the autophagic response that counteracts differentiation process.

Bridging the age spectrum of neurodegenerative storage diseases

For over a century, researchers have observed similar neurodegenerative hallmarks in brains of people affected by rare early-onset lysosomal storage diseases and late-onset neurodegenerative diseases such as Alzheimer's and Parkinson's disease. Increasing evidence suggests these apparently disparate diseases share a common underlying feature, namely, a dysfunctional clearance of cellular cargo through the secretory-endosomal-autophagic-lysosomal-exocytic (SEALE) network. By providing examples of rare and common neurodegenerative diseases known to have pathologically altered cargo flux through the SEALE network, we explore the unifying hypothesis that impaired catabolism or exocytosis of SEALE cargo, places a burden of stress on neurons that initiates pathogenesis. We also describe how a growing understanding of genetic, epigenetic and age-related modifications of the SEALE network, has inspired a number of novel disease-modifying therapeutic approaches aimed at alleviating SEALE storage and providing therapeutic benefit to people affected by these devastating diseases across the age spectrum.