Defects in trafficking bridge Parkinson's disease pathology and genetics. Nature. 2016;539:207-216. [PMID: 27830778 DOI: 10.1038/nature20414]

Patient-Specific iPSC-Derived Astrocytes Contribute to Non-Cell-Autonomous Neurodegeneration in Parkinson's Disease

Parkinson's disease (PD) is associated with the degeneration of ventral midbrain dopaminergic neurons (vmDAns) and the accumulation of toxic α-synuclein. A non-cell-autonomous contribution, in particular of astrocytes, during PD pathogenesis has been suggested by observational studies, but remains to be experimentally tested. Here, we generated induced pluripotent stem cell-derived astrocytes and neurons from familial mutant LRRK2 G2019S PD patients and healthy individuals. Upon co-culture on top of PD astrocytes, control vmDAns displayed morphological signs of neurodegeneration and abnormal, astrocyte-derived α-synuclein accumulation. Conversely, control astrocytes partially prevented the appearance of disease-related phenotypes in PD vmDAns. We additionally identified dysfunctional chaperone-mediated autophagy (CMA), impaired macroautophagy, and progressive α-synuclein accumulation in PD astrocytes. Finally, chemical enhancement of CMA protected PD astrocytes and vmDAns via the clearance of α-synuclein accumulation. Our findings unveil a crucial non-cell-autonomous contribution of astrocytes during PD pathogenesis, and open the path to exploring novel therapeutic strategies aimed at blocking the pathogenic cross talk between neurons and glial cells.

Micro- and nanotechnology approaches to improve Parkinson's disease therapy

Current therapies for Parkinson's disease are symptomatic and unable to regenerate the brain tissue. In recent years, the therapeutic potential of a wide variety of neuroprotective and neuroregenerative molecules such as neurotrophic factors, antioxidants and RNA-based therapeutics has been explored. However, drug delivery to the brain is still a challenge and the therapeutic efficacy of many drugs is limited. In the last decade, micro- and nanoparticles have proved to be powerful tools for the administration of these molecules to the brain, enabling the development of new strategies against Parkinson's disease. The list of encapsulated drugs and the nature of the particles used is long, and numerous studies have been carried out supporting their efficacy in treating this pathology. This review aims to give an overview of the latest advances and emerging frontiers in micro- and nanomedical approaches for repairing dopaminergic neurons. Special emphasis will be placed on offering a new perspective to link these advances with the most relevant clinical trials and with the real possibility of transferring micro- and nanoformulations to industrial scale-up processes. This review is intended as a contribution towards facing the challenges that still exist in the clinical translation of micro- and nanotechnologies to administer therapeutic agents in Parkinson's disease.

The Challenge to Search for New Nervous System Disease Biomarker Candidates: the Opportunity to Use the Proteogenomics Approach

Alzheimer's disease, Parkinson's disease, prion diseases, schizophrenia, and multiple sclerosis are the most common nervous system diseases, affecting millions of people worldwide. The current scientific literature associates these pathological conditions to abnormal expression levels of certain proteins, which in turn improved the knowledge concerning normal and affected brains. However, there is no available cure or preventive therapy for any of these disorders. Proteogenomics is a recent approach defined as the data integration of both nucleotide high-throughput sequencing and protein mass spectrometry technologies. In the last years, proteogenomics studies in distinct diseases have emerged as a strategy for the identification of uncharacterized proteoforms, which are all the different protein forms derived from a single gene. For many of these diseases, at least one protein used as biomarker presents more than one proteoform, which fosters the analysis of publicly available data focusing proteoforms. Given this context, we describe the most important biomarkers for each neurodegenerative disease and how genomics, transcriptomics, and proteomics separately contributed to unveil them. Finally, we present a selection of proteogenomics studies in which the combination of nucleotide and proteome high-throughput data, from cell lines or brain tissue samples, is used to uncover proteoforms not previously described. We believe that this new approach may improve our knowledge about nervous system diseases and brain function and an opportunity to identify new biomarker candidates.

Stem Cell Transplantation and Physical Exercise in Parkinson's Disease, a Literature Review of Human and Animal Studies

The absence of effective and satisfactory treatments that contribute to repairing the dopaminergic damage caused by Parkinson's Disease (PD) and the limited recovery capacity of the nervous system are troubling issues and the focus of many research and clinical domains. Recent advances in the treatment of PD through stem cell (SC) therapy have recognized their promising restorative and neuroprotective effects that are implicated in the potentiation of endogenous mechanisms of repair and contribute to functional locomotor improvement. Physical exercise (PE) has been considered an adjuvant intervention that by itself induces beneficial effects in patients and animal models with Parkinsonism. In this sense, the combination of both therapies could provide synergic or superior effects for motor recovery, in contrast with their individual use. This review aims to provide an update on recent progress and the potential effectiveness of SC transplantation and PE for the treatment of locomotor deficits in PD. It has reviewed the neuropathological pathways involved in the classical motor symptoms of this condition and the mechanisms of action described in experimental studies that are associated with locomotor enhancement through exercise, cellular transplantation, and their union in some neurodegenerative conditions.

Analysis of RNA Expression Profiles Identifies Dysregulated Vesicle Trafficking Pathways in Creutzfeldt-Jakob Disease

Functional genomics applied to the study of RNA expression profiles identified several abnormal molecular processes in experimental prion disease. However, only a few similar studies have been carried out to date in a naturally occurring human prion disease. To better characterize the transcriptional cascades associated with sporadic Creutzfeldt-Jakob disease (sCJD), the most common human prion disease, we investigated the global gene expression profile in samples from the frontal cortex of 10 patients with sCJD and 10 non-neurological controls by microarray analysis. The comparison identified 333 highly differentially expressed genes (hDEGs) in sCJD. Functional enrichment Gene Ontology analysis revealed that hDEGs were mainly associated with synaptic transmission, including GABA (q value = 0.049) and glutamate (q value = 0.005) signaling, and the immune/inflammatory response. Furthermore, the analysis of cellular components performed on hDEGs showed a compromised regulation of vesicle-mediated transport with mainly up-regulated genes related to the endosome (q value = 0.01), lysosome (q value = 0.04), and extracellular exosome (q value < 0.01). A targeted analysis of the retromer core component VPS35 (vacuolar protein sorting-associated protein 35) showed a down-regulation of gene expression (p value= 0.006) and reduced brain protein levels (p value= 0.002). Taken together, these results confirm and expand previous microarray expression profile data in sCJD. Most significantly, they also demonstrate the involvement of the endosomal-lysosomal system. Since the latter is a common pathogenic pathway linking together diseases, such as Alzheimer's and Parkinson's, it might be the focus of future studies aimed to identify new therapeutic targets in neurodegenerative diseases.

On cell death in the intestinal epithelium and its impact on gut homeostasis

PURPOSE OF REVIEW

Both apoptotic and nonapoptotic cell extrusion preserve the barrier functions of epithelia. Live cell extrusion is the paradigm for homeostatic renewal of intestinal epithelial cells (IEC). By extension, as extruded cells are not apoptotic, this form of cell shedding is thought to be largely ignored by lamina propria phagocytes and without immune consequence.

RECENT FINDINGS

Visualization of apoptotic IEC inside distinct subsets of intestinal phagocytes during homeostasis has highlighted apoptosis as a normal component of the natural turnover of the intestinal epithelium. Analysis of phagocytes with or without apoptotic IEC corpses has shown how apoptotic IEC constrain inflammatory pathways within phagocytes and induce immunosuppressive regulatory CD4 T-cell differentiation. Many of the genes involved overlap with susceptibility genes for inflammatory bowel disease (IBD).

SUMMARY

Excessive IEC death and loss-of-barrier function is characteristic of IBD. As regulatory and tolerogenic mechanisms are broken in IBD, a molecular understanding of the precise triggers and modes of IEC death as well as their consequences on intestinal inflammation is necessary. This characterization should guide new therapies that restore homeostatic apoptosis, along with its associated programs of immune tolerance and immunosuppression, to achieve mucosal healing and long-term remission.

Precisely measured protein lifetimes in the mouse brain reveal differences across tissues and subcellular fractions

The turnover of brain proteins is critical for organism survival, and its perturbations are linked to pathology. Nevertheless, protein lifetimes have been difficult to obtain in vivo. They are readily measured in vitro by feeding cells with isotopically labeled amino acids, followed by mass spectrometry analyses. In vivo proteins are generated from at least two sources: labeled amino acids from the diet, and non-labeled amino acids from the degradation of pre-existing proteins. This renders measurements difficult. Here we solved this problem rigorously with a workflow that combines mouse in vivo isotopic labeling, mass spectrometry, and mathematical modeling. We also established several independent approaches to test and validate the results. This enabled us to measure the accurate lifetimes of ~3500 brain proteins. The high precision of our data provided a large set of biologically significant observations, including pathway-, organelle-, organ-, or cell-specific effects, along with a comprehensive catalog of extremely long-lived proteins (ELLPs).

Measuring precise protein turnover rates in animals is technically challenging at the proteomic level. Here, Fornasiero and colleagues use isotopic labeling with mass spectrometry and mathematical modeling to accurately determine protein lifetimes in the mouse brain

Angiotensin Type 1 Receptor Antagonists Protect Against Alpha-Synuclein-Induced Neuroinflammation and Dopaminergic Neuron Death

The loss of dopaminergic neurons and α-synuclein accumulation are major hallmarks of Parkinson's disease (PD), and it has been suggested that a major mechanism of α-synuclein toxicity is microglial activation. The lack of animal models that properly reproduce PD, and particularly the underlying synucleinopathy, has hampered the clarification of PD mechanisms and the development of effective therapies. Here, we used neurospecific adeno-associated viral vectors serotype 9 coding for either the wild-type or mutated forms of human alpha-synuclein (WT and SynA53T, respectively) under the control of a synapsin promoter to further induce a marked dopaminergic neuron loss together with an important microglial neuroinflammatory response. Overexpression of neuronal alpha-synuclein led to increased expression of angiotensin type 1 receptors and NADPH oxidase activity, together with a marked increase in the number of OX-6-positive microglial cells and expression of markers of phagocytic activity (CD68) and classical pro-inflammatory/M1 microglial phenotype markers such as inducible nitric oxide synthase, tumor necrosis factor alpha, interleukin-1β, and IL-6. Moreover, a significant decrease in the expression of markers of immunoregulatory/M2 microglial phenotype such as the enzyme arginase-1 was constantly observed. Interestingly, alpha-synuclein-induced changes in microglial phenotype markers and dopaminergic neuron death were inhibited by simultaneous treatment with the angiotensin type 1 blockers candesartan or telmisartan. Our results suggest the repurposing of candesartan and telmisartan as a neuroprotective strategy for PD.

Alpha-synuclein delays mitophagy and targeting Miro rescues neuron loss in Parkinson's models

Alpha-synuclein is a component of Lewy bodies, the pathological hallmark of Parkinson's disease (PD), and is also mutated in familial PD. Here, by extensively analyzing PD patient brains and neurons, and fly models, we show that alpha-synuclein accumulation results in upregulation of Miro protein levels. Miro is a motor/adaptor on the outer mitochondrial membrane that mediates mitochondrial motility, and is removed from damaged mitochondria to facilitate mitochondrial clearance via mitophagy. PD patient neurons abnormally accumulate Miro on the mitochondrial surface leading to delayed mitophagy. Partial reduction of Miro rescues mitophagy phenotypes and neurodegeneration in human neurons and flies. Upregulation of Miro by alpha-synuclein requires an interaction via the N-terminus of alpha-synuclein. Our results highlight the importance of mitochondria-associated alpha-synuclein in human disease, and present Miro as a novel therapeutic target.

Converging pathways in neurodegeneration, from genetics to mechanisms

Neurodegenerative diseases cause progressive loss of cognitive and/or motor function and pose major challenges for societies with rapidly aging populations. Human genetics studies have shown that disease-causing rare mutations and risk-associated common alleles overlap in different neurodegenerative disorders. Here we review the intricate genotype-phenotype relationships and common cellular pathways emerging from recent genetic and mechanistic studies. Shared pathological mechanisms include defective protein quality-control and degradation pathways, dysfunctional mitochondrial homeostasis, stress granules, and maladaptive innate immune responses. Research efforts have started to bear fruit, as shown by recent treatment successes and an encouraging therapeutic outlook.

Adapting Secretory Proteostasis and Function Through the Unfolded Protein Response

Cells address challenges to protein folding in the secretory pathway by engaging endoplasmic reticulum (ER)-localized protective mechanisms that are collectively termed the unfolded protein response (UPR). By the action of the transmembrane signal transducers IRE1, PERK, and ATF6, the UPR induces networks of genes whose products alleviate the burden of protein misfolding. The UPR also plays instructive roles in cell differentiation and development, aids in the response to pathogens, and coordinates the output of professional secretory cells. These functions add to and move beyond the UPR's classical role in addressing proteotoxic stress. Thus, the UPR is not just a reaction to protein misfolding, but also a fundamental driving force in physiology and pathology. Recent efforts have yielded a suite of chemical genetic methods and small molecule modulators that now provide researchers with both stress-dependent and -independent control of UPR activity. Such tools provide new opportunities to perturb the UPR and thereby study mechanisms for maintaining proteostasis in the secretory pathway. Numerous observations now hint at the therapeutic potential of UPR modulation for diseases related to the misfolding and aggregation of ER client proteins. Growing evidence also indicates the promise of targeting ER proteostasis nodes downstream of the UPR. Here, we review selected advances in these areas, providing a resource to inform ongoing studies of secretory proteostasis and function as they relate to the UPR.

Parkinson's disease research: adopting a more human perspective to accelerate advances

Parkinson's disease (PD) affects 1% of the population over 60 years old and, with global increases in the aging population, presents huge economic and societal burdens. The etiology of PD remains unknown; most cases are idiopathic, presumed to result from genetic and environmental risk factors. Despite 200 years since the first description of PD, the mechanisms behind initiation and progression of the characteristic neurodegenerative processes are not known. Here, we review progress and limitations of the multiple PD animal models available and identify advances that could be implemented to better understand pathological processes, improve disease outcome, and reduce dependence on animal models. Lessons learned from reducing animal use in PD research could serve as guideposts for wider biomedical research.

Muskelin Coordinates PrPC Lysosome versus Exosome Targeting and Impacts Prion Disease Progression

Cellular prion protein (PrP^C) modulates cell adhesion and signaling in the brain. Conversion to its infectious isoform causes neurodegeneration, including Creutzfeldt-Jakob disease in humans. PrP^C undergoes rapid plasma membrane turnover and extracellular release via exosomes. However, the intracellular transport of PrP^C and its potential impact on prion disease progression is barely understood. Here we identify critical components of PrP^C trafficking that also link intracellular and extracellular PrP^C turnover. PrP^C associates with muskelin, dynein, and KIF5C at transport vesicles. Notably, muskelin coordinates bidirectional PrP^C transport and facilitates lysosomal degradation over exosomal PrP^C release. Muskelin gene knockout consequently causes PrP^C accumulation at the neuronal surface and on secreted exosomes. Moreover, prion disease onset is accelerated following injection of pathogenic prions into muskelin knockout mice. Our data identify an essential checkpoint in PrP^C turnover. They propose a novel connection between neuronal intracellular lysosome targeting and extracellular exosome trafficking, relevant to the pathogenesis of neurodegenerative conditions.

Determinants of dopaminergic neuron loss in Parkinson's disease

The cardinal motor symptoms of Parkinson's disease (PD) are caused by the death of dopaminergic neurons in the substantia nigra pars compacta (SNc). Alpha-synuclein (aSYN) pathology and mitochondrial dysfunction have been implicated in PD pathogenesis, but until recently it was unclear why SNc dopaminergic neurons should be particularly vulnerable to these two types of insult. In this brief review, the evidence that SNc dopaminergic neurons have an anatomical, physiological, and biochemical phenotype that predisposes them to mitochondrial dysfunction and synuclein pathology is summarized. The recognition that certain traits may predispose neurons to PD-linked pathology creates translational opportunities for slowing or stopping disease progression.

VPS13A and VPS13C are lipid transport proteins differentially localized at ER contact sites

Structural and biochemical studies show that VPS13 family proteins are lipid transporters. VPS13A and VPS13C tether the ER to mitochondria and to endosomes/lysosomes, respectively, suggesting lipid dyshomeostasis as the cause of chorea acanthocytosis and Parkinson’s disease resulting from their mutations.

Mutations in the human VPS13 genes are responsible for neurodevelopmental and neurodegenerative disorders including chorea acanthocytosis (VPS13A) and Parkinson’s disease (VPS13C). The mechanisms of these diseases are unknown. Genetic studies in yeast hinted that Vps13 may have a role in lipid exchange between organelles. In this study, we show that the N-terminal portion of VPS13 is tubular, with a hydrophobic cavity that can solubilize and transport glycerolipids between membranes. We also show that human VPS13A and VPS13C bind to the ER, tethering it to mitochondria (VPS13A), to late endosome/lysosomes (VPS13C), and to lipid droplets (both VPS13A and VPS13C). These findings identify VPS13 as a lipid transporter between the ER and other organelles, implicating defects in membrane lipid homeostasis in neurological disorders resulting from their mutations. Sequence and secondary structure similarity between the N-terminal portions of Vps13 and other proteins such as the autophagy protein ATG2 suggest lipid transport roles for these proteins as well.

A new hypothesis for Parkinson's disease pathogenesis: GTPase-p38 MAPK signaling and autophagy as convergence points of etiology and genomics

The combination of genetics and genomics in Parkinson´s disease has recently begun to unveil molecular mechanisms possibly underlying disease onset and progression. In particular, catabolic processes such as autophagy have been increasingly gaining relevance as post-mortem evidence and experimental models suggested a participation in neurodegeneration and alpha-synuclein Lewy body pathology. In addition, familial Parkinson´s disease linked to LRRK2 and alpha-synuclein provided stronger correlation between etiology and alterations in autophagy. More detailed cellular pathways are proposed and genetic risk factors that associate with idiopathic Parkinson´s disease provide further clues in dissecting contributions of single players. Nevertheless, the fine-tuning of these processes remains elusive, as the initial stages of the pathways are not yet clarified.In this review, we collect literature evidence pointing to autophagy as the common, downstream target of Parkinsonian dysfunctions and augment current knowledge on the factors that direct the subsequent steps. Cell and molecular biology evidence indicate that p38 signaling underlies neurodegeneration and autoptic observations suggest a participation in neuropathology. Moreover, alpha-synuclein and LRRK2 also appear involved in the p38 pathway with additional roles in the regulation of GTPase signaling. Small GTPases are critical modulators of p38 activation and thus, their functional interaction with aSyn and LRRK2 could explain much of the detailed mechanics of autophagy in Parkinson´s disease.We propose a novel hypothesis for a more comprehensive working model where autophagy is controlled by upstream pathways, such as GTPase-p38, that have been so far underexplored in this context. In addition, etiological factors (LRRK2, alpha-synuclein) and risk loci might also combine in this common mechanism, providing a powerful experimental setting to dissect the cause of both familial and idiopathic disease.

A Mutation in the Borcs7 Subunit of the Lysosome Regulatory BORC Complex Results in Motor Deficits and Dystrophic Axonopathy in Mice

Lysosomes play a critical role in maintenance of the integrity of neuronal function, and mutations in genes that contribute to lysosome formation, transport, and activity are associated with neurodegenerative disorders. Recently, the multisubunit complex, BLOC-one-related complex (BORC), has been shown to be involved in positioning lysosomes within the cytoplasm, although the consequences of altered BORC function in adult animals have not been established. We show that a spontaneous truncation mutation in the mouse Borcs7 gene, identified through whole-genome sequencing followed by genetic complementation, results in progressive axonal dystrophy with dramatic impairment of motor function. Furthermore, mice homozygous for deletion of the entire Borcs7 coding sequence die shortly after birth, and neurons cultured from these animals show impaired centrifugal transport of lysosomes. This identifies BORCS7 as a central factor in axonal transport of lysosomes and a possible target for improving disease-related disturbances in this important function.

Minimotifs dysfunction is pervasive in neurodegenerative disorders

Minimotifs are modular contiguous peptide sequences in proteins that are important for posttranslational modifications, binding to other molecules, and trafficking to specific subcellular compartments. Some molecular functions of proteins in cellular pathways can be predicted from minimotif consensus sequences identified through experimentation. While a role for minimotifs in regulating signal transduction and gene regulation during disease pathogenesis (such as infectious diseases and cancer) is established, the therapeutic use of minimotif mimetic drugs is limited. In this review, we discuss a general theme identifying a pervasive role of minimotifs in the pathomechanism of neurodegenerative diseases. Beyond their longstanding history in the genetics of familial neurodegeneration, minimotifs are also major players in neurotoxic protein aggregation, aberrant protein trafficking, and epigenetic regulation. Generalizing the importance of minimotifs in neurodegenerative diseases offers a new perspective for the future study of neurodegenerative mechanisms and the investigation of new therapeutics.

Prevention of progression in Parkinson's disease

Environmental influences affecting genetically susceptible individuals seem to contribute significantly to the development of Parkinson’s disease (PD). Xenobiotic exposure including transitional metal deposition into vulnerable CNS regions appears to interact with PD genes. Such exposure together with mitochondrial dysfunction evokes a destructive cascade of biochemical events, including oxidative stress and degeneration of the sensitive dopamine (DA) production system in the basal ganglia. Recent research indicates that the substantia nigra degeneration can be decelerated by treatment with iron binding compounds such as deferiprone. Interestingly compounds known to decrease PD risk including caffeine, niacin, nicotine and salbutamol also possess iron binding properties. Adequate function of antioxidative mechanisms in the vulnerable brain cells can be restored by acetylcysteine supplementation to normalize intracellular glutathione activity. Other preventive measures to reduce deterioration of dopaminergic neurons may involve life-style changes such as intake of natural antioxidants and physical exercise. Further research is recommended to identify therapeutic targets of the proposed interventions, in particular protection of the DA biosynthesis by oxygen radical scavengers and iron binding agents.

Convergent pathways in Parkinson's disease

Preferential degeneration of dopamine neurons (DAn) in the midbrain represents the principal hallmark of Parkinson's disease (PD). It has been hypothesized that major contributors to DAn vulnerability lie in their unique cellular physiology and architecture, which make them particularly susceptible to stress factors. Here, we report a concise overview of some of the cell mechanisms that may exacerbate DAn sensitivity and loss in PD. In particular, we highlight how defective protein sorting and clearance, endoplasmic reticulum stress, calcium dyshomeostasis and intracellular trafficking converge to contribute synergistically to neuronal dysfunction in PD pathogenesis.

Genetic risk factors in Parkinson's disease

Over the last two decades, we have witnessed a revolution in the field of Parkinson's disease (PD) genetics. Great advances have been made in identifying many loci that confer a risk for PD, which has subsequently led to an improved understanding of the molecular pathways involved in disease pathogenesis. Despite this success, it is predicted that only a relatively small proportion of the phenotypic variability has been explained by genetics. Therefore, it is clear that common heritable components of disease are still to be identified. Dissecting the genetic architecture of PD constitutes a critical effort in identifying therapeutic targets and although such substantial progress has helped us to better understand disease mechanism, the route to PD disease-modifying drugs is a lengthy one. In this review, we give an overview of the known genetic risk factors in PD, focusing not on individual variants but the larger networks that have been implicated following comprehensive pathway analysis. We outline the challenges faced in the translation of risk loci to pathobiological relevance and illustrate the need for integrating big-data by noting success in recent work which adopts a broad-scale screening approach. Lastly, with PD genetics now progressing from identifying risk to predicting disease, we review how these models will likely have a significant impact in the future.

Loss of Drosha underlies dopaminergic neuron toxicity in models of Parkinson's disease

MiRNAs, a group of powerful modulator of gene expression, participate in multiple cellular processes under physiological and pathological conditions. Emerging evidence shows that Drosha, which controls the initial step in canonical miRNA biogenesis, is involved in modulating cell survival and death in models of several diseases. However, the role of Drosha in Parkinson’s disease (PD) has not been well established. Here, we show that the level of Drosha decreases in 6-OHDA-induced cellular and animal models of PD. 6-OHDA induced a p38 MAPK-dependent phosphorylation of Drosha. This triggered Drosha degradation. Enhancing the level of Drosha protected the dopaminergic (DA) neurons from 6-OHDA-induced toxicity in both in vitro and in vivo models of PD and alleviated the motor deficits of PD mice. These findings reveal that Drosha plays a critical role in the survival of DA neurons and suggest that stress-induced destabilization of Drosha may be part of the pathological process in PD.

Targeting energy metabolism via the mitochondrial pyruvate carrier as a novel approach to attenuate neurodegeneration

Several molecular pathways are currently being targeted in attempts to develop disease-modifying therapies to slow down neurodegeneration in Parkinson’s disease. Failure of cellular energy metabolism has long been implicated in sporadic Parkinson’s disease and recent research on rare inherited forms of Parkinson’s disease have added further weight to the importance of energy metabolism in the disease pathogenesis. There exists a new class of anti-diabetic insulin sensitizers in development that inhibit the mitochondrial pyruvate carrier (MPC), a protein which mediates the import of pyruvate across the inner membrane of mitochondria. Pharmacological inhibition of the MPC was recently found to be strongly neuroprotective in multiple neurotoxin-based and genetic models of neurodegeneration which are relevant to Parkinson’s disease. In this review, we summarize the neuroprotective effects of MPC inhibition and discuss the potential putative underlying mechanisms. These mechanisms involve augmentation of autophagy via attenuation of the activity of the mammalian target of rapamycin (mTOR) in neurons, as well as the inhibition of neuroinflammation, which is at least partly mediated by direct inhibition of MPC in glia cells. We conclude that MPC is a novel and potentially powerful therapeutic target that warrants further study in attempts to slow Parkinson’s disease progression.

Autophagy in Age-Associated Neurodegeneration

The elimination of abnormal and dysfunctional cellular constituents is an essential prerequisite for nerve cells to maintain their homeostasis and proper function. This is mainly achieved through autophagy, a process that eliminates abnormal and dysfunctional cellular components, including misfolded proteins and damaged organelles. Several studies suggest that age-related decline of autophagy impedes neuronal homeostasis and, subsequently, leads to the progression of neurodegenerative disorders due to the accumulation of toxic protein aggregates in neurons. Here, we discuss the involvement of autophagy perturbation in neurodegeneration and present evidence indicating that upregulation of autophagy holds potential for the development of therapeutic interventions towards confronting neurodegenerative diseases in humans.

MiR-212 Attenuates MPP⁺-Induced Neuronal Damage by Targeting KLF4 in SH-SY5Y Cells

PURPOSE

Parkinson's disease (PD) is a common age-dependent neurodegenerative disease. MiR-212 has been demonstrated to exert protective effects in several neurological disorders. The present study aimed to investigate the role and underlying molecular mechanism of miR-212 in PD.

MATERIALS AND METHODS

1-methyl-4-phenylpyridinium (MPP+)-induced SH-SY5Y cells were applied as a PD model in vitro. RT-qPCR was used to measure the expression of miR-212 and Kruppel-like factor 4 (KLF4) mRNA. Western blot analysis was performed to detect the protein levels of KLF4, Notch1 and Jagged1. Cell viability and apoptosis were determined by the Cell Counting Kit-8 and flow cytometry, respectively. Quantitative analysis of caspase-3 activity, lactate dehydrogenase (LDH), reactive oxygen species (ROS), superoxide dismutase (SOD), tumor necrosis factor-α (TNF-α), and interleukin-1 beta (IL-1β) was conducted with corresponding ELISA kits. Dual-luciferase reporter assay was employed to evaluate the relationship between miR-212 and KLF4.

RESULTS

MiR-212 was downregulated in MPP⁺-induced SH-SY5Y cells. Also, miR-212 alleviated MPP⁺-induced SH-SY5Y cell damage, embodied by increased cell viability, decreased caspase-3 activity, LDH release, ROS production, TNF-α, and IL-1β expression, as well as elevated SOD levels. KLF4 was a direct target of miR-212, and miR-212 repressed KLF4 expression in a post-transcriptional manner. Moreover, miR-212-mediated protection effects were abated following KLF4 expression restoration in MPP⁺-induced SH-SY5Y cells, represented as lowered cell viability and enhanced apoptotic rate. Furthermore, Notch signaling was involved in the regulation of miR-212/KLF4 axis in MPP⁺-induced SH-SY5Y cells.

CONCLUSION

miR-212 might attenuate MPP⁺-induced neuronal damage by regulating KLF4/Notch signaling pathway in SH-SY5Y cells, a promising target for PD therapy.

The expression of KATP channel subunits in alpha-synuclein-transfected MES23.5 cells

Background

SUR1, one of the subunits of ATP-sensitive potassium (K_ATP) channels, was found to be highly expressed in mRNA levels in the substantia nigra (SN) of Parkinson's disease (PD) brains. Though the mechanism of the selective dopamine (DA) neurons death is still unknown, some studies have demonstrated that selective activation of the K_ATP channels in the SN might be associated with the degeneration of DA neurons. The objective of our study is to examine the expressions of K_ATP channel subunits in dopaminergic cells with alpha-synuclein (α-Syn) transfection.

Methods

In this study, we detected the K_ATP channel subunits mRNA levels in MES23.5 cells by real-time quantitative PCR after the cells transfected with α-Syn.

Results

Our results showed that the mRNA levels of SUR1 subunit were markedly increased by 35% in WT α-Syn overexpression cells and by 31% in A53T α-Syn overexpression cells, respectively. However, the mRNA levels of SUR2B and Kir6.2 subunit have no obviously differences from the controls.

Conclusions

We showed that the mRNA levels of SUR1 but not SUR2B or Kir6.2 were selectively upregulated in MES23.5 cells over-expressed with α-Syn. The findings demonstrated that the SUR1 overexpressed might be involved in the process of PD.

P62/SQSTM1 is a novel leucine-rich repeat kinase 2 (LRRK2) substrate that enhances neuronal toxicity

Autosomal-dominant, missense mutations in the leucine-rich repeat protein kinase 2 (LRRK2) gene are the most common genetic predisposition to develop Parkinson's disease (PD). LRRK2 kinase activity is increased in several pathogenic mutations (N1437H, R1441C/G/H, Y1699C, G2019S), implicating hyperphosphorylation of a substrate in the pathogenesis of the disease. Identification of the downstream targets of LRRK2 is a crucial endeavor in the field to understand LRRK2 pathway dysfunction in the disease. We have identified the signaling adapter protein p62/SQSTM1 as a novel endogenous interacting partner and a substrate of LRRK2. Using mass spectrometry and phospho-specific antibodies, we found that LRRK2 phosphorylates p62 on Thr138 in vitro and in cells. We found that the pathogenic LRRK2 PD-associated mutations (N1437H, R1441C/G/H, Y1699C, G2019S) increase phosphorylation of p62 similar to previously reported substrate Rab proteins. Notably, we found that the pathogenic I2020T mutation and the risk factor mutation G2385R displayed decreased phosphorylation of p62. p62 phosphorylation by LRRK2 is blocked by treatment with selective LRRK2 inhibitors in cells. We also found that the amino-terminus of LRRK2 is crucial for optimal phosphorylation of Rab7L1 and p62 in cells. LRRK2 phosphorylation of Thr138 is dependent on a p62 functional ubiquitin-binding domain at its carboxy-terminus. Co-expression of p62 with LRRK2 G2019S increases the neurotoxicity of this mutation in a manner dependent on Thr138. p62 is an additional novel substrate of LRRK2 that regulates its toxic biology, reveals novel signaling nodes and can be used as a pharmacodynamic marker for LRRK2 kinase activity.

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

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

Deregulation of autophagy and vesicle trafficking in Parkinson's disease

Parkinson's disease (PD) is a common neurodegenerative disease characterized pathologically by the selective loss of dopaminergic neurons in the substantia nigra and the intracellular accumulation of α-synuclein in the Lewy bodies. While the pathogenic mechanisms of PD are poorly understood, many lines of evidence point to a role of altered autophagy and membrane trafficking in the development of the disease. Emerging studies show that connections between the deregulation of autophagy and synaptic vesicle (SV) trafficking may contribute to PD. Here we review the evidence that many PD related-genes have roles in both autophagy and SV trafficking and examine how deregulation of these pathways contributes to PD pathogenesis. This review also discusses recent studies aimed at uncovering the role of PD-linked genes in autophagy-lysosome function.

Neuronal lysosomes

Lysosomes support diverse cellular functions by acting as sites of macromolecule degradation and nutrient recycling. The degradative abilities of lysosomes are conferred by a lumen that is characterized by an acidic pH and which contains numerous hydrolases that support the breakdown of major cellular macromolecules to yield cellular building blocks (amino acids, nucleic acids, sugars, lipids and metals) that are transported into the cytoplasm for their re-use. In addition to these important hydrolytic and recycling functions, lysosomes also serve as a signaling platform that integrates nutrient and metabolic cues to control signaling via the mTORC1 pathway. Due to their extreme longevity, polarity, demands of neurotransmission and metabolic activity, neurons are particularly sensitive to perturbations in lysosome function. The dependence of neurons on optimal lysosome function is highlighted by insights from human genetics that link lysosome dysfunction to a wide range of both rare and common neurological diseases. How then is lysosome function adapted to the unique demands of neurons? This review will focus on the roles played by lysosomes in distinct neuronal sub-compartments, the regulation of neuronal lysosome sub-cellular localization and the implications of such neuronal lysosome regulation for both physiology and disease.

Current perspective of mitochondrial biology in Parkinson's disease

Parkinson's disease (PD) is one of the most common neurodegenerative movement disorder characterized by preferential loss of dopaminergic neurons of the substantia nigra pars compacta and the presence of Lewy bodies containing α-synuclein. Although the cause of PD remains elusive, remarkable advances have been made in understanding the possible causative mechanisms of PD pathogenesis. An explosion of discoveries during the past two decades has led to the identification of several autosomal dominant and recessive genes that cause familial forms of PD. The investigations of these familial PD gene products have shed considerable insights into the molecular pathogenesis of the more common sporadic PD. A growing body of evidence suggests that the etiology of PD is multifactorial and involves a complex interplay between genetic and environmental factors. Substantial evidence from human tissues, genetic and toxin-induced animal and cellular models indicates that mitochondrial dysfunction plays a central role in the pathophysiology of PD. Deficits in mitochondrial functions due to bioenergetics defects, alterations in the mitochondrial DNA, generation of reactive oxygen species, aberrant calcium homeostasis, and anomalies in mitochondrial dynamics and quality control are implicated in the underlying mechanisms of neuronal cell death in PD. In this review, we discuss how familial PD-linked genes and environmental factors interface the pathways regulating mitochondrial functions and thereby potentially converge both familial and sporadic PD at the level of mitochondrial integrity. We also provide an overview of the status of therapeutic strategies targeting mitochondrial dysfunction in PD. Unraveling potential pathways that influence mitochondrial homeostasis in PD may hold the key to therapeutic intervention for this debilitating neurodegenerative movement disorder.

The hidden potential of lysosomal ion channels: A new era of oncogenes

Lysosomes serve as the control centre for cellular clearance. These membrane-bound organelles receive biomolecules destined for degradation from intracellular and extracellular pathways; thus, facilitating the production of energy and shaping the fate of the cell. At the base of their functionality are the lysosomal ion channels which mediate the function of the lysosome through the modulation of ion influx and efflux. Ion channels form pores in the membrane of lysosomes and allow the passage of ions, a seemingly simple task which harbours the potential of overthrowing the cell's stability. Considered the master regulators of ion homeostasis, these integral membrane proteins enable the proper operation of the lysosome. Defects in the structure or function of these ion channels lead to the development of lysosomal storage diseases, neurodegenerative diseases and cancer. Although more than 50 years have passed since their discovery, lysosomes are not yet fully understood, with their ion channels being even less well characterized. However, significant improvements have been made in the development of drugs targeted against these ion channels as a means of combating diseases. In this review, we will examine how Ca²⁺, K⁺, Na⁺ and Cl^- ion channels affect the function of the lysosome, their involvement in hereditary and spontaneous diseases, and current ion channel-based therapies.

Astaxanthin protects against kainic acid-induced seizures and pathological consequences

Excitotoxic damage caused by increased glutamate levels is involved in the pathogenesis of neurodegenerative diseases. Astaxanthin, a natural carotenoid with multiple health benefits, inhibits glutamate release from the brain tissue; however, whether it possesses the ability to affect glutamate-induced brain injury is unknown. The present study investigated the neuroprotective effects of astaxanthin on kainic acid (KA)-induced excitotoxicity in rats and the possible underlying intracellular signaling pathway. The rats were orally administrated with astaxanthin (50 or 100 mg/kg) for 7 days (once a day), and KA (15 mg/kg) was administered intraperitoneally at 1 h after the final administration. The results revealed that KA induced seizures, increased the hippocampal glutamate levels, caused considerable neuronal death and microglial activation in the hippocampal CA3 regions, and increased the production of proinflammatory cytokines. Astaxanthin pretreatment prevented these changes. Furthermore, astaxanthin pretreatment increased the expression of neuronal cell survival-related factors, including phosphorylated Akt, phosphorylated glycogen synthase kinase-3β, and Bcl-2 in the hippocampus of KA-injected rats. These results suggested that astaxanthin can attenuate seizures, mitigate inflammation, augment survival signals, and prevent hippocampal neuronal damage in the animal model of KA-induced excitotoxicity.

Mechanisms of α-Synuclein Induced Synaptopathy in Parkinson's Disease

Parkinson's disease (PD) is characterized by intracellular inclusions of aggregated and misfolded α-Synuclein (α-Syn), and the loss of dopaminergic (DA) neurons in the brain. The resulting motor abnormalities mark the progression of PD, while non-motor symptoms can already be identified during early, prodromal stages of disease. Recent studies provide evidence that during this early prodromal phase, synaptic and axonal abnormalities occur before the degenerative loss of neuronal cell bodies. These early phenotypes can be attributed to synaptic accumulation of toxic α-Syn. Under physiological conditions, α-Syn functions in its native conformation as a soluble monomer. However, PD patient brains are characterized by intracellular inclusions of insoluble fibrils. Yet, oligomers and protofibrils of α-Syn have been identified to be the most toxic species, with their accumulation at presynaptic terminals affecting several steps of neurotransmitter release. First, high levels of α-Syn alter the size of synaptic vesicle pools and impair their trafficking. Second, α-Syn overexpression can either misregulate or redistribute proteins of the presynaptic SNARE complex. This leads to deficient tethering, docking, priming and fusion of synaptic vesicles at the active zone (AZ). Third, α-Syn inclusions are found within the presynaptic AZ, accompanied by a decrease in AZ protein levels. Furthermore, α-Syn overexpression reduces the endocytic retrieval of synaptic vesicle membranes during vesicle recycling. These presynaptic alterations mediated by accumulation of α-Syn, together impair neurotransmitter exocytosis and neuronal communication. Although α-Syn is expressed throughout the brain and enriched at presynaptic terminals, DA neurons are the most vulnerable in PD, likely because α-Syn directly regulates dopamine levels. Indeed, evidence suggests that α-Syn is a negative modulator of dopamine by inhibiting enzymes responsible for its synthesis. In addition, α-Syn is able to interact with and reduce the activity of VMAT2 and DAT. The resulting dysregulation of dopamine levels directly contributes to the formation of toxic α-Syn oligomers. Together these data suggest a vicious cycle of accumulating α-Syn and deregulated dopamine that triggers synaptic dysfunction and impaired neuronal communication, ultimately causing synaptopathy and progressive neurodegeneration in Parkinson's disease.

Robust kinase- and age-dependent dopaminergic and norepinephrine neurodegeneration in LRRK2 G2019S transgenic mice

Mutations in LRRK2 are known to be the most common genetic cause of sporadic and familial Parkinson's disease (PD). Multiple lines of LRRK2 transgenic or knockin mice have been developed, yet none exhibit substantial dopamine (DA)-neuron degeneration. Here we develop human tyrosine hydroxylase (TH) promoter-controlled tetracycline-sensitive LRRK2 G2019S (GS) and LRRK2 G2019S kinase-dead (GS/DA) transgenic mice and show that LRRK2 GS expression leads to an age- and kinase-dependent cell-autonomous neurodegeneration of DA and norepinephrine (NE) neurons. Accompanying the loss of DA neurons are DA-dependent behavioral deficits and α-synuclein pathology that are also LRRK2 GS kinase-dependent. Transmission EM reveals that that there is an LRRK2 GS kinase-dependent significant reduction in synaptic vesicle number and a greater abundance of clathrin-coated vesicles in DA neurons. These transgenic mice indicate that LRRK2-induced DA and NE neurodegeneration is kinase-dependent and can occur in a cell-autonomous manner. Moreover, these mice provide a substantial advance in animal model development for LRRK2-associated PD and an important platform to investigate molecular mechanisms for how DA neurons degenerate as a result of expression of mutant LRRK2.

VPS35, the Retromer Complex and Parkinson's Disease

Mutations in the vacuolar protein sorting 35 ortholog (VPS35) gene encoding a core component of the retromer complex, have recently emerged as a new cause of late-onset, autosomal dominant familial Parkinson’s disease (PD). A single missense mutation, AspD620Asn (D620N), has so far been unambiguously identified to cause PD in multiple individuals and families worldwide. The exact molecular mechanism(s) by which VPS35 mutations induce progressive neurodegeneration in PD are not yet known. Understanding these mechanisms, as well as the perturbed cellular pathways downstream of mutant VPS35, is important for the development of appropriate therapeutic strategies. In this review, we focus on the current knowledge surrounding VPS35 and its role in PD. We provide a critical discussion of the emerging data regarding the mechanisms underlying mutant VPS35-mediated neurodegeneration gleaned from genetic cell and animal models and highlight recent advances that may provide insight into the interplay between VPS35 and several other PD-linked gene products (i.e. α-synuclein, LRRK2 and parkin) in PD. Present data support a role for perturbed VPS35 and retromer function in the pathogenesis of PD.

Parkinson disease-associated mutations in LRRK2 cause centrosomal defects via Rab8a phosphorylation

BACKGROUND

Mutations in LRRK2 are a common genetic cause of Parkinson's disease (PD). LRRK2 interacts with and phosphorylates a subset of Rab proteins including Rab8a, a protein which has been implicated in various centrosome-related events. However, the cellular consequences of such phosphorylation remain elusive.

METHODS

Human neuroblastoma SH-SY5Y cells stably expressing wildtype or pathogenic LRRK2 were used to test for polarity defects in the context of centrosomal positioning. Centrosomal cohesion deficits were analyzed from transiently transfected HEK293T cells, as well as from two distinct peripheral cell types derived from LRRK2-PD patients. Kinase assays, coimmunoprecipitation and GTP binding/retention assays were used to address Rab8a phosphorylation by LRRK2 and its effects in vitro. Transient transfections and siRNA experiments were performed to probe for the implication of Rab8a and its phosphorylated form in the centrosomal deficits caused by pathogenic LRRK2.

RESULTS

Here, we show that pathogenic LRRK2 causes deficits in centrosomal positioning with effects on neurite outgrowth, cell polarization and directed migration. Pathogenic LRRK2 also causes deficits in centrosome cohesion which can be detected in peripheral cells derived from LRRK2-PD patients as compared to healthy controls, and which are reversed upon LRRK2 kinase inhibition. The centrosomal cohesion and polarity deficits can be mimicked when co-expressing wildtype LRRK2 with wildtype but not phospho-deficient Rab8a. The centrosomal defects induced by pathogenic LRRK2 are associated with a kinase activity-dependent increase in the centrosomal localization of phosphorylated Rab8a, and are prominently reduced upon RNAi of Rab8a.

CONCLUSIONS

Our findings reveal a new function of LRRK2 mediated by Rab8a phosphorylation and related to various centrosomal defects.

Neuronal lysosomal dysfunction releases exosomes harboring APP C-terminal fragments and unique lipid signatures

Defects in endolysosomal and autophagic functions are increasingly viewed as key pathological features of neurodegenerative disorders. A master regulator of these functions is phosphatidylinositol-3-phosphate (PI3P), a phospholipid synthesized primarily by class III PI 3-kinase Vps34. Here we report that disruption of neuronal Vps34 function in vitro and in vivo impairs autophagy, lysosomal degradation as well as lipid metabolism, causing endolysosomal membrane damage. PI3P deficiency also promotes secretion of unique exosomes enriched for undigested lysosomal substrates, including amyloid precursor protein C-terminal fragments (APP-CTFs), specific sphingolipids, and the phospholipid bis(monoacylglycero)phosphate (BMP), which normally resides in the internal vesicles of endolysosomes. Secretion of these exosomes requires neutral sphingomyelinase 2 and sphingolipid synthesis. Our results reveal a homeostatic response counteracting lysosomal dysfunction via secretion of atypical exosomes eliminating lysosomal waste and define exosomal APP-CTFs and BMP as candidate biomarkers for endolysosomal dysfunction associated with neurodegenerative disorders.

Pla2g6 Deficiency in Zebrafish Leads to Dopaminergic Cell Death, Axonal Degeneration, Increased β-Synuclein Expression, and Defects in Brain Functions and Pathways

This study aimed to gain insights into the pathophysiology underlying PLA2G6-associated neurodegeneration that is implicated in three different neurological disorders, suggesting that other, unknown genetic or environmental factors might contribute to its wide phenotypic expression. To accomplish this, we downregulated the function of pla2g6 in the zebrafish nervous system, performed parkinsonism-related phenotypic characterization, and determined the effects of gene regulation upon the loss of pla2g6 function by using RNA sequencing and downstream analyses. Pla2g6 deficiency resulted in axonal degeneration, dopaminergic and motor neuron cell loss, and increased β-synuclein expression. We also observed that many of the identified, differentially expressed genes were implicated in other brain disorders, which might explain the variable phenotypic expression of pla2g6-associated disease, and found that top enriched canonical pathways included those already known or suggested to play a major role in the pathogenesis of Parkinson's disease. Our data support that pla2g6 is relevant for cranial motor development with significant implications in the pathophysiology underlying Parkinson's disease.

Mitochondrial ATP-sensitive potassium channel regulates mitochondrial dynamics to participate in neurodegeneration of Parkinson's disease

Parkinson's disease (PD) is the second most common age-related neurodegenerative disease. Mitochondrial dysfunction has been the focus of the pathogenesis of PD. The mitochondrial ATP-sensitive potassium channel (mitoKATP) plays a significant role in mitochondrial physiology and has been extensively shown to protect against ischemic and brain reperfusion injury. However, there have long been controversies regarding its role in Parkinson's disease. We investigated the role of mitoKATP channels in rotenone-induced PD model in vivo and vitro and the interactions of mitoKATP channels, mitochondrial dynamics and PD. The results indicated that the use of diazoxide to activate mitoKATP channels resulted in the aggravation of rotenone-induced dopamine neurodegeneration in PC12 cells and SD rats. In contrast, the use of 5-hydroxydecanoate (5-HD) to inhibit mitoKATP channels improved rotenone-induced dopamine neurodegeneration, which was not consistent with mitoKATP channels in ischemic and brain reperfusion injury. Further analysis determined that the mitoKATP channel was involved in PD mainly via the regulation of mitochondrial biogenesis and fission/fusion. And the pore subunits of Kir6.1, the major component of mitoKATP channels, was the key contributor in its interaction with mitochondrial dynamics in rotenone-induced dopamine neurodegeneration. Therefore, it can be concluded that mitoKATP channels regulate mitochondrial dynamics to participate in rotenone-induced PD mainly attributes to the pore subunits of Kir6.1. And additionally, though mitoKATP channels may represent a direction of one potential target for neuroprotection, it should be noted that the effects are different in the activation or inhibition of mitoKATP channels in different models.

Defective trafficking of Kv2.1 channels in MPTP-induced nigrostriatal degeneration

Intracellular protein trafficking is tightly regulated, and improper trafficking might be the fundamental provocateur for human diseases including neurodegeneration. In neurons, protein trafficking to and from the plasma membrane affects synaptic plasticity. Voltage-gated potassium channel 2.1 (Kv2.1) is a predominant delayed rectifier potassium (K⁺ ) current, and electrical activity patterns of dopamine (DA) neurons within the substantia nigra are generated and modulated by the orchestrated function of different ion channels. The pathological hallmark of Parkinson's disease (PD) is the progressive loss of these DA neurons, resulting in the degeneration of striatal dopaminergic terminals. However, whether trafficking of Kv2.1 channels contributes to PD remains unclear. In this study, we demonstrated that MPTP/MPP⁺ increases the surface expression of the Kv2.1 channel and causes nigrostriatal degeneration by using a subchronic MPTP mouse model. The inhibition of the Kv2.1 channel by using a specific blocker, guangxitoxin-1E, protected nigrostriatal projections against MPTP/MPP⁺ insult and thus facilitated the recovery of motor coordination. These findings highlight the importance of trafficking of Kv2.1 channels in the pathogenesis of PD.

DNAJC12 deficiency: A new strategy in the diagnosis of hyperphenylalaninemias

Patients with hyperphenylalaninemia (HPA) are detected through newborn screening for phenylketonuria (PKU). HPA is known to be caused by deficiencies of the enzyme phenylalanine hydroxylase (PAH) or its cofactor tetrahydrobiopterin (BH₄). Current guidelines for the differential diagnosis of HPA would, however, miss a recently described DNAJC12 deficiency. The co-chaperone DNAJC12 is, together with the 70kDa heat shock protein (HSP70), responsible for the proper folding of PAH. All DNAJC12-deficient patients investigated to date responded to a challenge with BH₄ by lowering their blood phenylalanine levels. In addition, the patients presented with low levels of biogenic amine in CSF and responded to supplementation with BH₄, L-dopa/carbidopa and 5-hydroxytryptophan. The phenotypic spectrum ranged from mild autistic features or hyperactivity to severe intellectual disability, dystonia and parkinsonism. Late diagnosis result in permanent neurological disability, while early diagnosed and treated patients develop normally. Molecular diagnostics for DNAJC12 variants are thus mandatory in all patients in which deficiencies of PAH and BH₄ are genetically excluded.

Towards diversity in genomics: The emergence of neurogenomics in Africa?

There is a high burden of mental and neurological disorders in Africa. Nevertheless, there appears to be an under-representation of African ancestry populations in large-scale genomic studies. Here, we evaluated the extent of under-representation of Africans in neurogenomic studies in the GWAS Catalog. We found 569 neurogenomic studies, of which 88.9% were exclusively focused on people with European ancestry and the remaining 11.1% having African ancestry cases included. In terms of population, only 1.2% of the total populations involved in these 569 GWAS studies were of African descent. Further, most of the individuals in the African ancestry category were identified to be African-Americans/Afro-Caribbeans, highlighting the huge under-representation of homogenous African populations in large-scale neurogenomic studies. Efforts geared at establishing strong collaborative ties with European/American researchers, maintaining freely accessible biobanks and establishing comprehensive African genome data repositories to track African genome variations are critical for propelling neurogenomics/precision medicine in Africa.

Activating Autophagy as a Therapeutic Strategy for Parkinson's Disease

Parkinson's disease is a progressive neurodegenerative disease characterized by Lewy body pathology of which the primary constituent is aggregated misfolded alpha-synuclein protein. Currently, there are no clinical therapies for treatment of the underlying alpha-synuclein dysfunction and accumulation, and the standard of care for patients with Parkinson's disease focuses only on symptom management, creating an immense therapeutic gap that needs to be filled. Defects in autophagy have been strongly implicated in Parkinson's disease. Here, we review evidence from human, mouse, and cell culture studies to briefly explain these defects in autophagy in Parkinson's disease and the necessity for autophagy to be carefully and precisely tuned to maintain neuron survival. We summarize recent experimental agents for treating alpha-synuclein accumulation in α-synuclein Parkinson's disease and related synucleinopathies. Most of the efforts for developing experimental agents have focused on immunotherapeutic strategies, but we discuss why those efforts are misplaced. Finally, we emphasize why increasing autophagy flux for alpha-synuclein clearance is the most promising therapeutic strategy. Activating autophagy has been successful in preclinical models of Parkinson's disease and yields promising results in clinical trials.

Autophagy in neurodegenerative diseases: pathogenesis and therapy

The most prevalent pathological features of many neurodegenerative diseases are the aggregation of misfolded proteins and the loss of certain neuronal populations. Autophagy, as major intracellular machinery for degrading aggregated proteins and damaged organelles, has been reported to be involved in the occurrence of pathological changes in many neurodegenerative disorders, including Alzheimer's disease, Parkinson's disease, Huntington's disease and amyotrophic lateral sclerosis. In this review, we summarize most recent research progress in this topic and provide a new perspective regarding autophagy regulation on the pathogenesis of neurodegenerative diseases. Finally, we discuss the signaling molecules in autophagy-related pathways as therapeutic targets for the treatment of these diseases.

Running wheel exercise reduces α-synuclein aggregation and improves motor and cognitive function in a transgenic mouse model of Parkinson's disease

Exercise has been recommended to improve motor function in Parkinson patients, but its value in altering progression of disease is unknown. In this study, we examined the neuroprotective effects of running wheel exercise in mice. In adult wild-type mice, one week of running wheel activity led to significantly increased DJ-1 protein concentrations in muscle and plasma. In DJ-1 knockout mice, running wheel performance was much slower and Rotarod performance was reduced, suggesting that DJ-1 protein is required for normal motor activity. To see if exercise can prevent abnormal protein deposition and behavioral decline in transgenic animals expressing a mutant human form of α-synuclein in all neurons, we set up running wheels in the cages of pre-symptomatic animals at 12 months old. Activity was monitored for a 3-month period. After 3 months, motor and cognitive performance on the Rotarod and Morris Water Maze were significantly better in running animals compared to control transgenic animals with locked running wheels. Biochemical analysis revealed that running mice had significantly higher DJ-1, Hsp70 and BDNF concentrations and had significantly less α-synuclein aggregation in brain compared to control mice. By contrast, plasma concentrations of α-synuclein were significantly higher in exercising mice compared to control mice. Our results suggest that exercise may slow the progression of Parkinson's disease by preventing abnormal protein aggregation in brain.

Synaptic phosphorylated α-synuclein in dementia with Lewy bodies

Dementia with Lewy bodies is characterized by the accumulation of Lewy bodies and Lewy neurites in the CNS, both of which are composed mainly of aggregated α-synuclein phosphorylated at Ser129. Although phosphorylated α-synuclein is believed to exert toxic effects at the synapse in dementia with Lewy bodies and other α-synucleinopathies, direct evidence for the precise synaptic localization has been difficult to achieve due to the lack of adequate optical microscopic resolution to study human synapses. In the present study we applied array tomography, a microscopy technique that combines ultrathin sectioning of tissue with immunofluorescence allowing precise identification of small structures, to quantitatively investigate the synaptic phosphorylated α-synuclein pathology in dementia with Lewy bodies. We performed array tomography on human brain samples from five patients with dementia with Lewy bodies, five patients with Alzheimer's disease and five healthy control subjects to analyse the presence of phosphorylated α-synuclein immunoreactivity at the synapse and their relationship with synapse size. Main analyses were performed in blocks from cingulate cortex and confirmed in blocks from the striatum of cases with dementia with Lewy bodies. A total of 1 318 700 single pre- or postsynaptic terminals were analysed. We found that phosphorylated α-synuclein is present exclusively in dementia with Lewy bodies cases, where it can be identified in the form of Lewy bodies, Lewy neurites and small aggregates (<0.16 µm3). Between 19% and 25% of phosphorylated α-synuclein deposits were found in presynaptic terminals mainly in the form of small aggregates. Synaptic terminals that co-localized with small aggregates of phosphorylated α-synuclein were significantly larger than those that did not. Finally, a gradient of phosphorylated α-synuclein aggregation in synapses (pre > pre + post > postsynaptic) was observed. These results indicate that phosphorylated α-synuclein is found at the presynaptic terminals of dementia with Lewy bodies cases mainly in the form of small phosphorylated α-synuclein aggregates that are associated with changes in synaptic morphology. Overall, our data support the notion that pathological phosphorylated α-synuclein may disrupt the structure and function of the synapse in dementia with Lewy bodies.