Increasing microtubule acetylation rescues axonal transport and locomotor deficits caused by LRRK2 Roc-COR domain mutations

Pyridine Dinucleotides from Molecules to Man

SIGNIFICANCE

Pyridine dinucleotides, nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP), were discovered more than 100 years ago as necessary cofactors for fermentation in yeast extracts. Since that time, these molecules have been recognized as fundamental players in a variety of cellular processes, including energy metabolism, redox homeostasis, cellular signaling, and gene transcription, among many others. Given their critical role as mediators of cellular responses to metabolic perturbations, it is unsurprising that dysregulation of NAD and NADP metabolism has been associated with the pathobiology of many chronic human diseases. Recent Advances: A biochemistry renaissance in biomedical research, with its increasing focus on the metabolic pathobiology of human disease, has reignited interest in pyridine dinucleotides, which has led to new insights into the cell biology of NAD(P) metabolism, including its cellular pharmacokinetics, biosynthesis, subcellular localization, and regulation. This review highlights these advances to illustrate the importance of NAD(P) metabolism in the molecular pathogenesis of disease.

CRITICAL ISSUES

Perturbations of NAD(H) and NADP(H) are a prominent feature of human disease; however, fundamental questions regarding the regulation of the absolute levels of these cofactors and the key determinants of their redox ratios remain. Moreover, an integrated topological model of NAD(P) biology that combines the metabolic and other roles remains elusive.

FUTURE DIRECTIONS

As the complex regulatory network of NAD(P) metabolism becomes illuminated, sophisticated new approaches to manipulating these pathways in specific organs, cells, or organelles will be developed to target the underlying pathogenic mechanisms of disease, opening doors for the next generation of redox-based, metabolism-targeted therapies. Antioxid. Redox Signal. 28, 180-212.

GTP binding regulates cellular localization of Parkinson's disease-associated LRRK2

Mutations in leucine-rich repeat kinase 2 (LRRK2) comprise the most common cause of familial Parkinson's disease (PD), and sequence variants modify risk for sporadic PD. Previous studies indicate that LRRK2 interacts with microtubules (MTs) and alters MT-mediated vesicular transport processes. However, the molecular determinants within LRRK2 required for such interactions have remained unknown. Here, we report that most pathogenic LRRK2 mutants cause relocalization of LRRK2 to filamentous structures which colocalize with a subset of MTs, and an identical relocalization is seen upon pharmacological LRRK2 kinase inhibition. The pronounced colocalization with MTs does not correlate with alterations in LRRK2 kinase activity, but rather with increased GTP binding. Synthetic mutations which impair GTP binding, as well as LRRK2 GTP-binding inhibitors profoundly interfere with the abnormal localization of both pathogenic mutant as well as kinase-inhibited LRRK2. Conversely, addition of a non-hydrolyzable GTP analog to permeabilized cells enhances the association of pathogenic or kinase-inhibited LRRK2 with MTs. Our data elucidate the mechanism underlying the increased MT association of select pathogenic LRRK2 mutants or of pharmacologically kinase-inhibited LRRK2, with implications for downstream MT-mediated transport events.

G2019S LRRK2 enhances the neuronal transmission of tau in the mouse brain

Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene cause late-onset, autosomal dominant Parkinson's disease (PD). LRRK2 mutations typically give rise to Lewy pathology in the brains of PD subjects yet can induce tau-positive neuropathology in some cases. The pathological interaction between LRRK2 and tau remains poorly defined. To explore this interaction in vivo, we crossed a well-characterized human P301S-tau transgenic mouse model of tauopathy with human G2019S-LRRK2 transgenic mice or LRRK2 knockout (KO) mice. We find that endogenous or pathogenic LRRK2 expression has minimal effects on the steady-state levels, solubility and abnormal phosphorylation of human P301S-tau throughout the mouse brain. We next developed a new model of tauopathy by delivering AAV2/6 vectors expressing human P301S-tau to the hippocampal CA1 region of G2019S-LRRK2 transgenic or LRRK2 KO mice. P301S-tau expression induces hippocampal tau pathology and marked degeneration of CA1 pyramidal neurons in mice, however, this occurs independently of endogenous or pathogenic LRRK2 expression. We further developed new AAV2/6 vectors co-expressing human WT-tau and GFP to monitor the neuron-to-neuron transmission of tau within defined hippocampal neuronal circuits. While endogenous LRRK2 is not required for tau transmission, we find that G2019S-LRRK2 markedly enhances the neuron-to-neuron transmission of tau in mice. Our data suggest that mutant tau-induced neuropathology occurs independently of LRRK2 expression in two mouse models of tauopathy but identifies a novel pathogenic role for G2019S-LRRK2 in promoting the neuronal transmission of WT-tau protein. These findings may have important implications for understanding the development of tau neuropathology in LRRK2-linked PD brains.

Endolysosomal dysfunction in Parkinson's disease: Recent developments and future challenges

Increasingly, genetic, cell biological, and in vivo work emphasizes the role of the endolysosomal system dysfunction in Parkinson's disease pathogenesis. Yet many questions remain about the mechanisms by which primary endolysosomal dysfunction causes PD as well as how the endolysosomal system interacts with α-synuclein-mediated neurotoxicity. We recently described a new mouse model of parkinsonism in which loss of the endolysosomal protein Atp13a2 causes behavioral, neuropathological, and biochemical changes similar to those present in human subjects with ATP13A2 mutations. In this Scientific Perspectives, we revisit the evidence implicating the endolysosomal system in PD, current hypotheses of disease pathogenesis, and how recent studies refine these hypotheses and raise new questions for future research. © 2016 International Parkinson and Movement Disorder Society.

Translational approaches to restoring mitochondrial function in Parkinson's disease

There is strong evidence of a key role for mitochondrial dysfunction in both sporadic and all forms of familial Parkinson's disease (PD). However, none of the clinical trials carried out with putative mitochondrial rescue agents have been successful. Firm establishment of a wet biomarker or a reliable readout from imaging studies detecting mitochondrial dysfunction and reflecting disease progression is also awaited. We will provide an overview of our current knowledge about mitochondrial dysfunction in PD and related drug screens. We will also summarise previously undertaken mitochondrial wet biomarker studies and relevant imaging studies with particular focus on 31P-MRI spectroscopy. We will conclude with an overview of clinical trials which tested putative mitochondrial rescue agents in PD patients.

Mitochondria: A Common Target for Genetic Mutations and Environmental Toxicants in Parkinson's Disease

Parkinson's disease (PD) is a devastating neurological movement disorder. Since its first discovery 200 years ago, genetic and environmental factors have been identified to play a role in PD development and progression. Although genetic studies have been the predominant driving force in PD research over the last few decades, currently only a small fraction of PD cases can be directly linked to monogenic mutations. The remaining cases have been attributed to other risk associated genes, environmental exposures and gene-environment interactions, making PD a multifactorial disorder with a complex etiology. However, enormous efforts from global research have yielded significant insights into pathogenic mechanisms and potential therapeutic targets for PD. This review will highlight mitochondrial dysfunction as a common pathway involved in both genetic mutations and environmental toxicants linked to PD.

Decreased Sirtuin Deacetylase Activity in LRRK2 G2019S iPSC-Derived Dopaminergic Neurons

Mitochondrial changes have long been implicated in the pathogenesis of Parkinson's disease (PD). The glycine to serine mutation (G2019S) in leucine-rich repeat kinase 2 (LRRK2) is the most common genetic cause for PD and has been shown to impair mitochondrial function and morphology in multiple model systems. We analyzed mitochondrial function in LRRK2 G2019S induced pluripotent stem cell (iPSC)-derived neurons to determine whether the G2019S mutation elicits similar mitochondrial deficits among central and peripheral nervous system neuron subtypes. LRRK2 G2019S iPSC-derived dopaminergic neuron cultures displayed unique abnormalities in mitochondrial distribution and trafficking, which corresponded to reduced sirtuin deacetylase activity and nicotinamide adenine dinucleotide levels despite increased sirtuin levels. These data indicate that mitochondrial deficits in the context of LRRK2 G2019S are not a global phenomenon and point to distinct sirtuin and bioenergetic deficiencies intrinsic to dopaminergic neurons, which may underlie dopaminergic neuron loss in PD.

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LRRK2 G2019S iPSC-derived dopaminergic neurons have unique mitochondrial defects

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LRRK2 G2019S dopaminergic neurons have increased sirtuin levels but reduced activity

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LRRK2 G2019S dopaminergic neurons have reduced NAD⁺ levels compared with other neurons

HDAC6 inhibition reverses axonal transport defects in motor neurons derived from FUS-ALS patients

Amyotrophic lateral sclerosis (ALS) is a rapidly progressive neurodegenerative disorder due to selective loss of motor neurons (MNs). Mutations in the fused in sarcoma (FUS) gene can cause both juvenile and late onset ALS. We generated and characterized induced pluripotent stem cells (iPSCs) from ALS patients with different FUS mutations, as well as from healthy controls. Patient-derived MNs show typical cytoplasmic FUS pathology, hypoexcitability, as well as progressive axonal transport defects. Axonal transport defects are rescued by CRISPR/Cas9-mediated genetic correction of the FUS mutation in patient-derived iPSCs. Moreover, these defects are reproduced by expressing mutant FUS in human embryonic stem cells (hESCs), whereas knockdown of endogenous FUS has no effect, confirming that these pathological changes are mutant FUS dependent. Pharmacological inhibition as well as genetic silencing of histone deacetylase 6 (HDAC6) increase α-tubulin acetylation, endoplasmic reticulum (ER)–mitochondrial overlay, and restore the axonal transport defects in patient-derived MNs.

Amyotrophic lateral sclerosis (ALS) leads to selective loss of motor neurons. Using motor neurons derived from induced pluripotent stem cells from patients with ALS and FUS mutations, the authors demonstrate that axonal transport deficits that are observed in these cells can be rescued by HDAC6 inhibition.

Neuron and microglia/macrophage-derived FGF10 activate neuronal FGFR2/PI3K/Akt signaling and inhibit microglia/macrophages TLR4/NF-κB-dependent neuroinflammation to improve functional recovery after spinal cord injury

Therapeutics used to treat central nervous system (CNS) injury were designed to repair neurites and inhibit cell apoptosis. Previous studies have shown that neuron-derived FGF10 exerts potential neuroprotective effects after cerebral ischemia injury. However, little is known about the role of endogenous FGF10 in the recovery process after spinal cord injury (SCI). In this study, we found that FGF10 is mainly produced by neuron and microglia/macrophages, and its expression is increased after SCI. Exogenous treatment of FGF10 improved functional recovery after injury by reducing apoptosis, as well as repairing neurites via FGFR2/PI3K/Akt pathway. On another hand, inhibiting the PI3K/Akt pathway with LY294002 partially reversed the therapeutic effects of FGF10. In addition, small interfering RNA knockdown of FGFR2 suppressed PI3K/Akt pathway activation by FGF10 and abolished its anti-apoptotic and neurite repair effects in vitro. Furthermore, FGF10 treatment inhibited the activation and proliferation of microglia/macrophages through regulation of TLR4/NF-κB pathway, and attenuated the release of pro-inflammatory cytokines after SCI. Thus, the increased expression of FGF10 after acute SCI is an endogenous self-protective response, suggesting that FGF10 could be a potential treatment for CNS injury.

Parkin absence accelerates microtubule aging in dopaminergic neurons

Loss-of-function caused by mutations in the parkin gene (PARK2) lead to early-onset familial Parkinson's disease. Recently, mechanistic studies proved the ability of parkin in regulating mitochondria homeostasis and microtubule (MT) stability. Looking at these systems during aging of PARK2 knockout mice, we found that loss of parkin induced an accelerated (over)acetylation of MT system both in dopaminergic neuron cell bodies and fibers, localized in the substantia nigra and corpus striatum, respectively. Interestingly, in PARK2 knockout mice, changes of MT stability preceded the alteration of mitochondria transport. Moreover, in-cell experiments confirmed that loss of parkin affects mitochondria mobility and showed that this defect depends on MT system as it is rescued by paclitaxel, a well-known MT-targeted agent. Furthermore, both in PC12 neuronal cells and in patients' induced pluripotent stem cell-derived midbrain neurons, we observed that parkin deficiencies cause the fragmentation of stable MTs. Therefore, we suggest that parkin acts as a regulator of MT system during neuronal aging, and we endorse the hypothesis that MT dysfunction may be crucial in the pathogenesis of Parkinson's disease.

Drosophila MIC60/mitofilin conducts dual roles in mitochondrial motility and crista structure

Mitochondria are crucial organelles for providing energy for a cell. It is known that MIC60/mitofilin is important for maintaining mitochondrial structure in dissociated cells; however, its physiological roles in an intact animal are less clear. In this study, we unravel the functional consequences of deleting MIC60/mitofilin in fruit flies.

MIC60/mitofilin constitutes a hetero-oligomeric complex on the inner mitochondrial membranes to maintain crista structure. However, little is known about its physiological functions. Here, by characterizing Drosophila MIC60 mutants, we define its roles in vivo. We discover that MIC60 performs dual functions to maintain mitochondrial homeostasis. In addition to its canonical role in crista membrane structure, MIC60 regulates mitochondrial motility, likely by influencing protein levels of the outer mitochondrial membrane protein Miro that anchors mitochondria to the microtubule motors. Loss of MIC60 causes loss of Miro and mitochondrial arrest. At a cellular level, loss of MIC60 disrupts synaptic structure and function at the neuromuscular junctions. The dual roles of MIC60 in both mitochondrial crista structure and motility position it as a crucial player for cellular integrity and survival.

Liraglutide activates autophagy via GLP-1R to improve functional recovery after spinal cord injury

Therapeutics used to treat central nervous system (CNS) injury are designed to promote axonal regeneration and inhibit cell death. Previous studies have shown that liraglutide exerts potent neuroprotective effects after brain injury. However, little is known if liraglutide treatment has neuroprotective effects after spinal cord injury (SCI). This study explores the neuroprotective effects of liraglutide and associated underlying mechanisms. Our results showed that liraglutide could improve recovery after injury by decreasing apoptosis as well as increasing microtubulin acetylation, and autophagy. Autophagy inhibition with 3-methyladenine (3-MA) partially reversed the preservation of spinal cord tissue and decreased microtubule acetylation and polymerization. Additionally, siRNA knockdown of GLP-1R suppressed autophagy and reversed mTOR inhibition induced by liraglutide in vitro, indicating that GLP-1R regulates autophagic flux. GLP-1R knockdown ameliorated the mTOR inhibition and autophagy induction seen with liraglutide treatment in PC12 cells under H₂O₂ stimulation. Taken together, our study demonstrated that liraglutide could reduce apoptosis, improve functional recovery, and increase microtubule acetylation via autophagy stimulation after SCI. GLP-1R was associated with both the induction of autophagy and suppression of apoptosis in neuronal cultures.

Neurobiology of axonal transport defects in motor neuron diseases: Opportunities for translational research?

Intracellular trafficking of cargoes is an essential process to maintain the structure and function of all mammalian cell types, but especially of neurons because of their extreme axon/dendrite polarisation. Axonal transport mediates the movement of cargoes such as proteins, mRNA, lipids, membrane-bound vesicles and organelles that are mostly synthesised in the cell body and in doing so is responsible for their correct spatiotemporal distribution in the axon, for example at specialised sites such as nodes of Ranvier and synaptic terminals. In addition, axonal transport maintains the essential long-distance communication between the cell body and synaptic terminals that allows neurons to react to their surroundings via trafficking of for example signalling endosomes. Axonal transport defects are a common observation in a variety of neurodegenerative diseases, and mutations in components of the axonal transport machinery have unequivocally shown that impaired axonal transport can cause neurodegeneration (reviewed in El-Kadi et al., 2007, De Vos et al., 2008; Millecamps and Julien, 2013). Here we review our current understanding of axonal transport defects and the role they play in motor neuron diseases (MNDs) with a specific focus on the most common form of MND, amyotrophic lateral sclerosis (ALS).

LRRK2: from kinase to GTPase to microtubules and back

Mutations in the Leucine-Rich Repeat Kinase 2 (LRRK2) gene are intimately linked to both familial and sporadic Parkinson's disease. LRRK2 is a large protein kinase able to bind and hydrolyse GTP. A wealth of in vitro studies have established that the distinct pathogenic LRRK2 mutants differentially affect those enzymatic activities, either causing an increase in kinase activity without altering GTP binding/GTP hydrolysis, or displaying no change in kinase activity but increased GTP binding/decreased GTP hydrolysis. Importantly, recent studies have shown that all pathogenic LRRK2 mutants display increased kinase activity towards select kinase substrates when analysed in intact cells. To understand those apparently discrepant results, better insight into the cellular role(s) of normal and pathogenic LRRK2 is crucial. Various studies indicate that LRRK2 regulates numerous intracellular vesicular trafficking pathways, but the mechanism(s) by which the distinct pathogenic mutants may equally interfere with such pathways has largely remained elusive. Here, we summarize the known alterations in the catalytic activities of the distinct pathogenic LRRK2 mutants and propose a testable working hypothesis by which the various mutants may affect membrane trafficking events in identical ways by culminating in increased phosphorylation of select substrate proteins known to be crucial for membrane trafficking between specific cellular compartments.

Cellular functions of LRRK2 implicate vesicular trafficking pathways in Parkinson's disease

Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene, associated with Parkinson's disease, have been shown to affect intracellular trafficking pathways in a variety of cells and organisms. An emerging theme is that LRRK2 can bind to multiple membranous structures in cells, and several recent studies have suggested that the Rab family of small GTPases might be important in controlling the recruitment of LRRK2 to specific cellular compartments. Once localized to membranes, LRRK2 then influences downstream events, evidenced by changes in the autophagy-lysosome pathway. Here, I will discuss available evidence that supports or challenges this outline, with a specific emphasis on those aspects of LRRK2 function that have been controversial or remain to be fully clarified.

Effect of Intrastriatal 6-OHDA Lesions on Extrastriatal Brain Structures in the Mouse

Parkinson's disease (PD) is a neurodegenerative disorder characterized by progressive loss of midbrain dopaminergic neurons, resulting in motor and non-motor symptoms. The underlying pathology of non-motor symptoms is poorly understood. Discussed are pathological changes of extrastriatal brain structures. In this study, we characterized histopathological alterations of extrastriatal brain structures in the 6-hydroxydopamine (6-OHDA) PD animal model. Lesions were induced by unilateral stereotactic injections of 6-OHDA into the striatum or medial forebrain bundle of adult male mice. Loss of tyrosine hydroxylase positive (TH⁺) fibers as well as glia activation was quantified following stereological principles. Loss of dopaminergic innervation was further investigated by western-blotting. As expected, 6-OHDA injection into the nigrostriatal route induced retrograde degeneration of dopaminergic neurons within the substantia nigra pars compacta (SNpc), less so within the ventral tegmental area. Furthermore, we observed a region-specific drop of TH⁺ projection fiber density in distinct cortical regions. This pathology was most pronounced in the cingulate- and motor cortex, whereas the piriform cortex was just modestly affected. Loss of cortical TH⁺ fibers was not paralleled by microglia or astrocyte activation. Our results demonstrate that the loss of dopaminergic neurons within the substantia nigra pars compacta is paralleled by a cortical dopaminergic denervation in the 6-OHDA model. This model serves as a valuable tool to investigate mechanisms operant during cortical pathology in PD patients. Further studies are needed to understand why cortical dopaminergic innervation is lost in this model, and what functional consequence is associated with the observed denervation.

Role of LRRK2 in the regulation of dopamine receptor trafficking

Mutations in LRRK2 play a critical role in both familial and sporadic Parkinson’s disease (PD). Up to date, the role of LRRK2 in PD onset and progression remains largely unknown. However, experimental evidence highlights a critical role of LRRK2 in the control of vesicle trafficking that in turn may regulate different aspects of neuronal physiology. We have analyzed the role of LRRK2 in regulating dopamine receptor D1 (DRD1) and D2 (DRD2) trafficking. DRD1 and DRD2 are the most abundant dopamine receptors in the brain. They differ in structural, pharmacological and biochemical properties, as well as in localization and internalization mechanisms. Our results indicate that disease-associated mutant G2019S LRRK2 impairs DRD1 internalization, leading to an alteration in signal transduction. Moreover, the mutant forms of LRRK2 affect receptor turnover by decreasing the rate of DRD2 trafficking from the Golgi complex to the cell membrane. Collectively, our findings are consistent with the conclusion that LRRK2 influences the motility of neuronal vesicles and the neuronal receptor trafficking. These findings have important implications for the complex role that LRRK2 plays in neuronal physiology and the possible pathological mechanisms that may lead to neuronal death in PD.

The interplay between histone deacetylases and rho kinases is important for cancer and neurodegeneration

Rho associated coiled-coil containing kinases (ROCKs) respond to defined extra- and intracellular stimuli to control cell migration, cell proliferation, and apoptosis. Histone deacetylases (HDACs) are epigenetic modifiers that regulate nuclear and cytoplasmic signaling through the deacetylation of histones and non-histone proteins. ROCK and HDAC functions are important compounds of basic and applied research interests. Recent evidence suggests a physiologically important interplay between HDACs and ROCKs in various cells and organisms. Here we summarize the crosstalk between these enzymatic families and its implications for cancer and neurodegeneration.

Targeting LRRK2 in Parkinson's disease: an update on recent developments

INTRODUCTION

LRRK2 research has progressed significantly in recent years with more reports of LRRK2 interactors and the development of more specific and sophisticated LRRK2 kinase inhibitors. Identification of bone fide LRRK2 substrates will provide new therapeutic targets in LRRK2-linked Parkinson's disease (PD). Areas covered: This review aims to put current LRRK2 research into perspective. Beginning with recent LRRK2 mammalian models employed for in vivo validation of LRRK2 substrates, followed by updates on reported LRRK2 interactors and their inferred mechanisms. Finally an overview of commonly used LRRK2 kinase inhibitors will be depicted. Expert opinion: Identification of LRRK2 non-kinase functions suggests the possibility of alternative LRRK2 drug target sites and these should be further explored. Studies on the effects of LRRK2 kinase inhibition on its non-kinase function and its self-regulatory role will provide further insights on its pathophysiologic mechanisms. Development of robust measurements of LRRK2 inhibitor efficacy will be required. These would include identification of specific imaging ligands or direct biochemical assays that can accurately capture its intrinsic activity. Testing of new therapeutic drug targets in both LRRK2 carriers and non LRRK2-linked patients will be important since their phenotype is similar.

Distinctive genomic signature of neural and intestinal organoids from familial Parkinson's disease patient-derived induced pluripotent stem cells

AIMS

The leucine-rich repeat kinase 2 (LRRK2) G2019S mutation is the most common genetic cause of Parkinson's disease (PD). There is compelling evidence that PD is not only a brain disease but also a gastrointestinal disorder; nonetheless, its pathogenesis remains unclear. We aimed to develop human neural and intestinal tissue models of PD patients harbouring an LRRK2 mutation to understand the link between LRRK2 and PD pathology by investigating the gene expression signature.

METHODS

We generated PD patient-specific induced pluripotent stem cells (iPSCs) carrying an LRRK2 G2019S mutation (LK2GS) and then differentiated into three-dimensional (3D) human neuroectodermal spheres (hNESs) and human intestinal organoids (hIOs). To unravel the gene and signalling networks associated with LK2GS, we analysed differentially expressed genes in the microarray data by functional clustering, gene ontology (GO) and pathway analyses.

RESULTS

The expression profiles of LK2GS were distinct from those of wild-type controls in hNESs and hIOs. The most represented GO biological process in hNESs and hIOs was synaptic transmission, specifically synaptic vesicle trafficking, some defects of which are known to be related to PD. The results were further validated in four independent PD-specific hNESs and hIOs by microarray and qRT-PCR analysis.

CONCLUSION

We provide the first evidence that LK2GS also causes significant changes in gene expression in the intestinal cells. These hNES and hIO models from the same genetic background of PD patients could be invaluable resources for understanding PD pathophysiology and for advancing the complexity of in vitro models with 3D expandable organoids.

Microtubule-Targeting Agents Eribulin and Paclitaxel Differentially Affect Neuronal Cell Bodies in Chemotherapy-Induced Peripheral Neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN) is a common side effect of anticancer treatment with microtubule-targeted agents (MTAs). The frequency of severe CIPN, which can be dose limiting and even life threatening, varies widely among different MTAs. For example, paclitaxel induces a higher frequency of severe CIPN than does eribulin. Different MTAs also possess distinct mechanisms of microtubule-targeted action. Recently, we demonstrated that paclitaxel and eribulin differentially affect sciatic nerve axons, with paclitaxel inducing more pronounced neurodegenerative effects and eribulin inducing greater microtubule stabilizing biochemical effects. Here, we complement and extend these axonal studies by assessing the effects of paclitaxel and eribulin in the cell bodies of sciatic nerve axons, housed in the dorsal root ganglia (DRG). Importantly, the microtubule network in cell bodies is known to be significantly more dynamic than in axons. Paclitaxel induced activating transcription factor 3 expression, a marker of neuronal stress/injury. Paclitaxel also increased expression levels of acetylated tubulin and end binding protein 1, markers of microtubule stability and growth, respectively. These effects are hypothesized to be detrimental to the dynamic microtubule network within the cell bodies. In contrast, eribulin had no significant effect on any of these parameters in the cell bodies. Taken together, DRG cell bodies and their axons, two distinct neuronal cell compartments, contain functionally distinct microtubule networks that exhibit unique biochemical responses to different MTA treatments. We hypothesize that these distinct mechanistic actions may underlie the variability seen in the initiation, progression, persistence, and recovery from CIPN.

Spastin regulates VAMP7-containing vesicles trafficking in cortical neurons

Alteration of axonal transport has emerged as a common precipitating factor in several neurodegenerative disorders including Human Spastic Paraplegia (HSP). Mutations of the SPAST (SPG4) gene coding for the spastin protein account for 40% of all autosomal dominant uncomplicated HSP. By cleaving microtubules, spastin regulates several cellular processes depending on microtubule dynamics including intracellular membrane trafficking. Axonal transport is fundamental for the viability of motor neurons which often have very long axons and thus require efficient communication between the cell body and its periphery. Here we found that the anterograde velocity of VAMP7 vesicles, but not that of VAMP2, two vesicular-SNARE proteins implicated in neuronal development, is enhanced in SPG4-KO neurons. We showed that this effect is associated with a slight increase of the level of acetylated tubulin in SPG4-KO neurons and correlates with an enhanced activity of kinesin-1 motors. Interestingly, we demonstrated that an artificial increase of acetylated tubulin by drugs reproduces the effect of Spastin KO on VAMP7 axonal dynamics but also increased its retrograde velocity. Finally, we investigated the effect of microtubule targeting agents which rescue axonal swellings, on VAMP7 and microtubule dynamics. Our results suggest that microtubule stabilizing agents, such as taxol, may prevent the morphological defects observed in SPG4-KO neurons not simply by restoring the altered anterograde transport to basal levels but rather by increasing the retrograde velocity of axonal cargoes.

Development of Improved HDAC6 Inhibitors as Pharmacological Therapy for Axonal Charcot-Marie-Tooth Disease

Charcot-Marie-Tooth disease (CMT) is the most common inherited peripheral neuropathy, with an estimated prevalence of 1 in 2500. The degeneration of motor and sensory nerve axons leads to motor and sensory symptoms that progress over time and have an important impact on the daily life of these patients. Currently, there is no curative treatment available. Recently, we identified histone deacetylase 6 (HDAC6), which deacetylates α-tubulin, as a potential therapeutic target in axonal CMT (CMT2). Pharmacological inhibition of the deacetylating function of HDAC6 reversed the motor and sensory deficits in a mouse model for mutant "small heat shock protein B1" (HSPB1)-induced CMT2 at the behavioral and electrophysiological level. In order to translate this potential therapeutic strategy into a clinical application, small drug-like molecules that are potent and selective HDAC6 inhibitors are essential. To screen for these, we developed a method that consisted of 3 distinct phases and that was based on the pathological findings in the mutant HSPB1-induced CMT2 mouse model. Three different inhibitors (ACY-738, ACY-775, and ACY-1215) were tested and demonstrated to be both potent and selective HDAC6 inhibitors. Moreover, these inhibitors increased the innervation of the neuromuscular junctions in the gastrocnemius muscle and improved the motor and sensory nerve conduction, confirming that HDAC6 inhibition is a potential therapeutic strategy in CMT2. Furthermore, ACY-1215 is an interesting lead molecule as it is currently tested in clinical trials for cancer. Taken together, these results may speed up the translation of pharmacological inhibition of HDAC6 into a therapy against CMT2.

Contribution of Neuroepigenetics to Huntington's Disease

Unbalanced epigenetic regulation is thought to contribute to the progression of several neurodegenerative diseases, including Huntington’s disease (HD), a genetic disorder considered as a paradigm of epigenetic dysregulation. In this review, we attempt to address open questions regarding the role of epigenetic changes in HD, in the light of recent advances in neuroepigenetics. We particularly discuss studies using genome-wide scale approaches that provide insights into the relationship between epigenetic regulations, gene expression and neuronal activity in normal and diseased neurons, including HD neurons. We propose that cell-type specific techniques and 3D-based methods will advance knowledge of epigenome in the context of brain region vulnerability in neurodegenerative diseases. A better understanding of the mechanisms underlying epigenetic changes and of their consequences in neurodegenerative diseases is required to design therapeutic strategies more effective than current strategies based on histone deacetylase (HDAC) inhibitors. Researches in HD may play a driving role in this process.

68 and FX2149 Attenuate Mutant LRRK2-R1441C-Induced Neural Transport Impairment

Leucine-rich repeat kinase 2 is a large protein with implications in genetic and sporadic causes of Parkinson's disease. The physiological functions of LRRK2 are largely unknown. In this report, we investigated whether LRRK2 alters neural transport using live-cell imaging techniques and human neuroblastoma SH-SY5Y cells. Our results demonstrated that expression of the PD-linked mutant, LRRK2-R1441C, induced mitochondrial, and lysosomal transport defects in neurites of SH-SY5Y cells. Most importantly, recently identified GTP-binding inhibitors, 68 and FX2149, can reduce LRRK2 GTP-binding activity and attenuates R1441C-induced mitochondrial and lysosomal transport impairments. These results provide direct evidence and an early mechanism for neurite injury underlying LRRK2-induced neurodegeneration. This is the first report to show that LRRK2 GTP-binding activity plays a critical role during neurite transport, suggesting inhibition of LRRK2 GTP-binding could be a potential novel strategy for PD intervention.

Phosphatidylserine improves axonal transport by inhibition of HDAC and has potential in treatment of neurodegenerative diseases

Familial dysautonomia (FD) is a rare children neurodegenerative disease caused due to a point mutation in the IKBKAP gene that results in decreased IKK complex-associated protein (IKAP) protein production. The disease affects mostly the dorsal root ganglion (DRG) and the sympathetic ganglion. Recently, we found that the molecular mechanisms underlying neurodegeneration in FD patients are defects in axonal transport of nerve growth factors and microtubule stability in the DRG. Neurons are highly polarized cells with very long axons. In order to survive and maintain proper function, neurons depend on transport of proteins and other cellular components from the neuronal body along the axons. We further demonstrated that IKAP is necessary for axon maintenance and showed that phosphatidylserine acts as an HDAC6 inhibitor to rescue neuronal function in FD cells. In this review, we will highlight our latest research findings.

Models of LRRK2-Associated Parkinson's Disease

Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene are the most common genetic causes of Parkinson's disease (PD) and also one of the strongest genetic risk factors in sporadic PD. The LRRK2 protein contains a GTPase and a kinase domain and several protein-protein interaction domains. Both in vitro and in vivo assays in different model systems have provided tremendous insights into the molecular mechanisms underlying LRRK2-induced dopaminergic neurodegeneration. Among all the model systems, animal models are crucial tools to study the pathogenesis of human disease. How do the animal models recapitulate LRRK2-induced dopaminergic neuronal loss in human PD? To answer this question, this review focuses on the discussion of the animal models of LRRK2-associated PD including genetic- and viral-based models.

Understanding the GTPase Activity of LRRK2: Regulation, Function, and Neurotoxicity

Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene are the most frequent cause of Parkinson's disease (PD) with late-onset and autosomal-dominant inheritance. LRRK2 belongs to the ROCO superfamily of proteins, characterized by a Ras-of-complex (Roc) GTPase domain in tandem with a C-terminal-of-Roc (COR) domain. LRRK2 also contains a protein kinase domain adjacent to the Roc-COR tandem domain in addition to multiple repeat domains. Disease-causing familial mutations cluster within the Roc-COR tandem and kinase domains of LRRK2, where they act to either impair GTPase activity or enhance kinase activity. Familial LRRK2 mutations share in common the capacity to induce neuronal toxicity in cultured cells. While the contribution of the frequent G2019S mutation, located within the kinase domain, to kinase activity and neurotoxicity has been extensively investigated, the contribution of GTPase activity has received less attention. The GTPase domain has been shown to play an important role in regulating kinase activity, in dimerization, and in mediating the neurotoxic effects of LRRK2. Accordingly, the GTPase domain has emerged as a potential therapeutic target for inhibiting the pathogenic effects of LRRK2 mutations. Many important mechanisms remain to be elucidated, including how the GTPase cycle of LRRK2 is regulated, whether GTPase effectors exist for LRRK2, and how GTPase activity contributes to the overall functional output of LRRK2. In this review, we discuss the importance of the GTPase domain for LRRK2-linked PD focusing in particular on its regulation, function, and contribution to neurotoxic mechanisms.

HDAC6 Inhibitors Rescued the Defective Axonal Mitochondrial Movement in Motor Neurons Derived from the Induced Pluripotent Stem Cells of Peripheral Neuropathy Patients with HSPB1 Mutation

The Charcot-Marie-Tooth disease 2F (CMT2F) and distal hereditary motor neuropathy 2B (dHMN2B) are caused by autosomal dominantly inherited mutations of the heat shock 27 kDa protein 1 (HSPB1) gene and there are no specific therapies available yet. Here, we assessed the potential therapeutic effect of HDAC6 inhibitors on peripheral neuropathy with HSPB1 mutation using in vitro model of motor neurons derived from induced pluripotent stem cells (iPSCs) of CMT2F and dHMN2B patients. The absolute velocity of mitochondrial movements and the percentage of moving mitochondria in axons were lower both in CMT2F-motor neurons and in dHMN2B-motor neurons than those in controls, and the severity of the defective mitochondrial movement was different between the two disease models. CMT2F-motor neurons and dHMN2B-motor neurons also showed reduced α-tubulin acetylation compared with controls. The newly developed HDAC6 inhibitors, CHEMICAL X4 and CHEMICAL X9, increased acetylation of α-tubulin and reversed axonal movement defects of mitochondria in CMT2F-motor neurons and dHMN2B-motor neurons. Our results suggest that the neurons derived from patient-specific iPSCs can be used in drug screening including HDAC6 inhibitors targeting peripheral neuropathy.

Screening for chemical modulators for LRRK2

After the discovery of leucine-rich repeat kinase 2 (LRRK2) as a risk factor for sporadic Parkinson's disease (PD) and mutations in LRRK2 as a cause of some forms of familial PD, there has been substantial interest in finding chemical modulators of LRRK2 function. Most of the pathogenic mutations in LRRK2 are within the enzymatic cores of the protein; therefore, many screens have focused on finding chemical modulators of this enzymatic activity. There are alternative screening approaches that could be taken to investigate compounds that modulate LRRK2 cellular functions. These screens are more often phenotypic screens. The preparation for a screen has to be rigorous and enable high-throughput accurate assessment of a compound's activity. The pipeline to beginning a drug screen and some LRRK2 inhibitor and phenotypic screens will be discussed.

SIRT2 regulates nuclear envelope reassembly through ANKLE2 deacetylation

Sirtuin 2 (SIRT2) is an NAD-dependent deacetylase known to regulate microtubule dynamics and cell cycle progression. SIRT2 has also been implicated in the pathology of cancer, neurodegenerative diseases and progeria. Here, we show that SIRT2 depletion or overexpression causes nuclear envelope reassembly defects. We link this phenotype to the recently identified regulator of nuclear envelope reassembly ANKLE2. ANKLE2 acetylation at K302 and phosphorylation at S662 are dynamically regulated throughout the cell cycle by SIRT2 and are essential for normal nuclear envelope reassembly. The function of SIRT2 therefore extends beyond the regulation of microtubules to include the regulation of nuclear envelope dynamics.

Mechanism of microtubule lumen entry for the α-tubulin acetyltransferase enzyme αTAT1

Microtubules are structural polymers inside of cells that are subject to posttranslational modifications. These posttranslational modifications create functionally distinct subsets of microtubule networks in the cell, and acetylation is the only modification that takes place in the hollow lumen of the microtubule. Although it is known that the α-tubulin acetyltransferase (αTAT1) is the primary enzyme responsible for microtubule acetylation, the mechanism for how αTAT1 enters the microtubule lumen to access its acetylation sites is not well understood. By performing biochemical assays, fluorescence and electron microscopy experiments, and computational simulations, we found that αTAT1 enters the microtubule lumen through the microtubule ends, and through bends or breaks in the lattice. Thus, microtubule structure is an important determinant in the acetylation process. In addition, once αTAT1 enters the microtubule lumen, the mobility of αTAT1 within the lumen is controlled by the affinity of αTAT1 for its acetylation sites, due to the rapid rebinding of αTAT1 onto highly concentrated α-tubulin acetylation sites. These results have important implications for how acetylation could gradually accumulate on stable subsets of microtubules inside of the cell.

Microtubule Destabilization Paves the Way to Parkinson's Disease

Microtubules are dynamic structures normally associated to the cell division, during which they form the mitotic spindle, as well as to the initial phases of specification and polarization of various cell types, including neurons. Although microtubules could have a role in the death of many cells and tissues, the microtubule-based degenerative mechanisms have been poorly investigated; nevertheless, during the last two decades, many clues have been accumulated suggesting the importance of the microtubule system during neurodegeneration. Thus, the aim of this review is to analyse how the changes of the microtubule cytoskeleton, in terms of organization and dynamics, as well as the failure of the microtubule-dependent neuronal processes, as axonal transport, may play a pivotal role in the chain of events leading to Parkinson's disease. Last but not least, since disease-modifying or neuroprotective strategies are a clinical priority in Parkinson's disease, we will also present the hints about the concrete possibility of a microtubule-targeted therapy, which would have the potentiality to block the running degenerative events and to prompt the regeneration of the lost tissues.

Back to the tubule: microtubule dynamics in Parkinson's disease

Cytoskeletal homeostasis is essential for the development, survival and maintenance of an efficient nervous system. Microtubules are highly dynamic polymers important for neuronal growth, morphology, migration and polarity. In cooperation with several classes of binding proteins, microtubules regulate long-distance intracellular cargo trafficking along axons and dendrites. The importance of a delicate interplay between cytoskeletal components is reflected in several human neurodegenerative disorders linked to abnormal microtubule dynamics, including Parkinson’s disease (PD). Mounting evidence now suggests PD pathogenesis might be underlined by early cytoskeletal dysfunction. Advances in genetics have identified PD-associated mutations and variants in genes encoding various proteins affecting microtubule function including the microtubule-associated protein tau. In this review, we highlight the role of microtubules, their major posttranslational modifications and microtubule associated proteins in neuronal function. We then present key evidence on the contribution of microtubule dysfunction to PD. Finally, we discuss how regulation of microtubule dynamics with microtubule-targeting agents and deacetylase inhibitors represents a promising strategy for innovative therapeutic development.

Emerging (and converging) pathways in Parkinson's disease: keeping mitochondrial wellness

The selective cell loss in the ventral component of the substantia nigra pars compacta and the presence of alpha-synuclein (α-syn)-rich intraneuronal inclusions called Lewy bodies are the pathological hallmarks of Parkinson's disease (PD), the most common motor system disorder whose aetiology remains largely elusive. Although most cases of PD are idiopathic, there are rare familial forms of the disease that can be traced to single gene mutations that follow Mendelian inheritance pattern. The study of several nuclear encoded proteins whose mutations are linked to the development of autosomal recessive and dominant forms of familial PD enhanced our understanding of biochemical and cellular mechanisms contributing to the disease and suggested that many signs of neurodegeneration result from compromised mitochondrial function. Here we present an overview of the current understanding of PD-related mitochondrial dysfunction including defects in bioenergetics and Ca²⁺ homeostasis, mitochondrial DNA mutations, altered mitochondrial dynamics and autophagy. We emphasize, in particular, the convergence of many "apparently" different pathways towards a common route involving mitochondria. Understanding whether mitochondrial dysfunction in PD represents the cause or the consequence of the disease is challenging and will help to define the pathogenic processes at the basis of the PD onset and progression.

Mechanisms of Parkinson's Disease: Lessons from Drosophila

The power of Drosophila genetics has attracted attention in tackling important biomedical challenges such as the understanding and prevention of neurodegenerative diseases. Parkinson's disease (PD) is the most common neurodegenerative movement disorder which results from the relentless degeneration of midbrain dopaminergic neurons. Over the past two decades tremendous advances have been made in identifying genes responsible for inherited forms of PD. The ease of genetic manipulation in Drosophila has spurred the development of numerous models of PD, including expression of human genes carrying pathogenic mutations or the targeted mutation of conserved orthologs. The genetic and cellular analysis of these models is beginning to reveal fundamental insights into the pathogenic mechanisms. Numerous pathways and processes are disrupted in these models but some common themes are emerging. These often implicate aberrant synaptic function, protein aggregation, autophagy, oxidative stress, and mitochondrial dysfunction. Moreover, an impressive list of small molecule compounds have been identified as effective in reversing pathogenic phenotypes, paving the way to explore these for therapeutic interventions.

LRRK2 at the Crossroad Between Autophagy and Microtubule Trafficking: Insights into Parkinson's Disease

Mutations in leucine-rich repeat kinase 2 ( lrrk2) gene cause inherited Parkinson's disease (PD), and common variants in lrrk2 are a risk factor for sporadic PD. The neuropathology associated with LRRK2-linked PD is extremely pleomorphic involving inclusions of α-synuclein (SNCA), tau or neither, therefore suggesting that LRRK2 may be central in the pathogenic pathways of PD. This large protein localizes in the cytosol, as well as, in specific membrane domains, including mitochondria and autophagosomes and interacts with a wide range of proteins such as SNCA, tau, α- and β-tubulin. For this reason LRRK2 has been associated with a variety of cellular functions, including autophagy, mitochondrial function/dynamics and microtubule/cytoskeletal dynamics. LRRK2 has been shown to interact with microtubules as well as with mitochondria interfering with their network and dynamics. Moreover, LRRK2 knock-out or mutations affect autophagic efficiency. Here, we review and discuss the literature on how LRRK2 affects mitochondrial function, autophagy, and microtubule dynamics and how this is implicated in the PD etiology.

The growing landscape of tubulin acetylation: lysine 40 and many more

Tubulin heterodimers are the building block of microtubules, which are major elements of the cytoskeleton. Several types of post-translational modifications are found on tubulin subunits as well as on the microtubule polymer to regulate the multiple roles of microtubules. Acetylation of lysine 40 (K40) of the α-tubulin subunit is one of these post-translational modifications which has been extensively studied. We summarize the current knowledge about the structural aspects of K40 acetylation, the functional consequences, the enzymes involved and their regulation. Most importantly, we discuss the potential importance of the recently discovered additional acetylation acceptor lysines in tubulin subunits and highlight the urgent need to study tubulin acetylation in a more integrated perspective.

An update on potential therapeutic strategies for Parkinson's disease based on pathogenic mechanisms

INTRODUCTION

Parkinson's disease is a common neurodegenerative disorder mainly caused by the loss of nigral dopaminergic neurons, of which the pathogenesis remains essentially unknown. Current therapeutic strategies help manage signs and symptoms but have no effect in disease modification. Over the past several decades, scientists have devoted a lot of effort to clarifying the pathological mechanism and searching for new targets for Parkinson's disease treatment.

AREAS COVERED

Treatment of Parkinson's disease. Expert Commentary: Illustrated in this review are newly found discoveries and evidence that contribute to the understanding of Parkinson's disease pathogenic mechanism. Also discussed are potential therapeutic strategies that are being studied, including disease-modifying and genetically mediated small molecule compounds, cell- and gene-based therapeutic strategies, immunization strategies and anti-diabetic therapy, which may be very promising therapeutic methods in the future.

Axonal transport defects are a common phenotype in Drosophila models of ALS

Amyotrophic lateral sclerosis (ALS) is characterized by the degeneration of motor neurons resulting in a catastrophic loss of motor function. Current therapies are severely limited owing to a poor mechanistic understanding of the pathobiology. Mutations in a large number of genes have now been linked to ALS, including SOD1, TARDBP (TDP-43), FUS and C9orf72. Functional analyses of these genes and their pathogenic mutations have provided great insights into the underlying disease mechanisms. Defective axonal transport is hypothesized to be a key factor in the selective vulnerability of motor nerves due to their extraordinary length and evidence that ALS occurs as a distal axonopathy. Axonal transport is seen as an early pathogenic event that precedes cell loss and clinical symptoms and so represents an upstream mechanism for therapeutic targeting. Studies have begun to describe the impact of a few pathogenic mutations on axonal transport but a broad survey across a range of models and cargos is warranted. Here, we assessed the axonal transport of different cargos in multiple Drosophila models of ALS. We found that axonal transport defects are common across all models tested, although they often showed a differential effect between mitochondria and vesicle cargos. Motor deficits were also common across the models and generally worsened with age, though surprisingly there was not a clear correlation between the severity of axonal transport defects and motor ability. These results further support defects in axonal transport as a common factor in models of ALS that may contribute to the pathogenic process.

5-((3-Amidobenzyl)oxy)nicotinamides as Sirtuin 2 Inhibitors

Derived from our previously reported human sirtuin 2 (SIRT2) inhibitors that were based on a 5-aminonaphthalen-1-yloxy nicotinamide core structure, 5-((3-amidobenzyl)oxy)nicotinamides offered excellent activity against SIRT2 and high isozyme selectivity over SIRT1 and SIRT3. Selected compounds also exhibited generally favorable in vitro absorption, distribution, metabolism, and excretion properties. Kinetic studies revealed that a representative SIRT2 inhibitor acted competitively against both NAD(+) and the peptide substrate, an inhibitory modality that was supported by our computational study. More importantly, two selected compounds exhibited significant protection against α-synuclein aggregation-induced cytotoxicity in SH-SY5Y cells. Therefore, 5-((3-amidobenzyl)oxy)nicotinamides represent a new class of SIRT2 inhibitors that are attractive candidates for further lead optimization in our continued effort to explore selective inhibition of SIRT2 as a potential therapy for Parkinson's disease.

LRRK2 Kinase Inhibition as a Therapeutic Strategy for Parkinson's Disease, Where Do We Stand?

One of the most promising therapeutic targets for potential disease-modifying treatment of Parkinson's disease (PD) is leucine-rich repeat kinase 2 (LRRK2). Specifically, targeting LRRK2's kinase function has generated a lot of interest from both industry and academia. This work has yielded several published studies showing the feasibility of developing potent, selective and brain permeable LRRK2 kinase inhibitors. The availability of these experimental drugs is contributing to filling in the gaps in our knowledge on the safety and efficacy of LRRK2 kinase inhibition. Recent studies of LRRK2 kinase inhibition in preclinical models point to potential undesired effects in peripheral tissues such as lung and kidney. Also, while strategies are now emerging to measure target engagement of LRRK2 inhibitors, there remains an important need to expand efficacy studies in preclinical models of progressive PD. Future work in the LRRK2 inhibition field must therefore be directed towards developing molecules and treatment regimens which demonstrate efficacy in mammalian models of disease in conditions where safety liabilities are reduced to a minimum.

Epothilone D prevents binge methamphetamine-mediated loss of striatal dopaminergic markers

Exposure to binge methamphetamine (METH) can result in a permanent or transient loss of dopaminergic (DAergic) markers such as dopamine (DA), dopamine transporter, and tyrosine hydroxylase (TH) in the striatum. We hypothesized that the METH-induced loss of striatal DAergic markers was, in part, due to a destabilization of microtubules (MTs) in the nigrostriatal DA pathway that ultimately impedes anterograde axonal transport of these markers. To test this hypothesis, adult male Sprague-Dawley rats were treated with binge METH or saline in the presence or absence of epothilone D (EpoD), a MT-stabilizing compound, and assessed 3 days after the treatments for the levels of several DAergic markers as well as for the levels of tubulins and their post-translational modifications (PMTs). Binge METH induced a loss of stable long-lived MTs within the striatum but not within the substantia nigra pars compacta (SNpc). Treatment with a low dose of EpoD increased the levels of markers of stable MTs and prevented METH-mediated deficits in several DAergic markers in the striatum. In contrast, administration of a high dose of EpoD appeared to destabilize MTs and potentiated the METH-induced deficits in several DAergic markers. The low-dose EpoD also prevented the METH-induced increase in striatal DA turnover and increased behavioral stereotypy during METH treatment. Together, these results demonstrate that MT dynamics plays a role in the development of METH-induced losses of several DAergic markers in the striatum and may mediate METH-induced degeneration of terminals in the nigrostriatal DA pathway. Our study also demonstrates that MT-stabilizing drugs such as EpoD have a potential to serve as useful therapeutic agents to restore function of DAergic nerve terminals following METH exposure when administered at low doses. Administration of binge methamphetamine (METH) negatively impacts neurotransmission in the nigrostriatal dopamine (DA) system. The effects of METH include decreasing the levels of DAergic markers in the striatum. We have determined that high-dose METH destabilizes microtubules in this pathway, which is manifested by decreased levels of acetylated (Acetyl) and detyrosinated (Detyr) α-tubulin (I). A microtubule stabilizing agent epothilone D protects striatal microtubules form the METH-induced loss of DAergic markers (II). These findings provide a new strategy for protection form METH - restoration of proper axonal transport.

Reducing Lissencephaly-1 levels augments mitochondrial transport and has a protective effect in adult Drosophila neurons

Defective transport of mitochondria in axons is implicated in the pathogenesis of several age-associated neurodegenerative diseases. However, the regulation and function of axonal mitochondrial motility during normal ageing is poorly understood. Here, we use novel imaging procedures to characterise axonal transport of these organelles in the adult Drosophila wing nerve. During early adult life there is a boost and progressive decline in the proportion of mitochondria that are motile, which is not due to general changes in cargo transport. Experimental inhibition of the mitochondrial transport machinery specifically in adulthood accelerates the appearance of focal protein accumulations in ageing axons, which is suggestive of defects in protein homeostasis. Unexpectedly, lowering levels of Lissencephaly-1 (Lis1), a dynein motor co-factor, augments axonal mitochondrial transport in ageing wing neurons. Lis1 mutations suppress focal protein accumulations in ageing neurons, including those caused by interfering with the mitochondrial transport machinery. Our data provide new insights into the dynamics of mitochondrial motility in adult neurons in vivo, identify Lis1 as a negative regulator of transport of these organelles, and provide evidence of a link between mitochondrial movement and neuronal protein homeostasis.

Summary: Novel imaging procedures in the adult Drosophila wing reveal that Lissencephaly-1 restrains mitochondrial motion and that reducing levels of this protein protects against an age-related decline in protein homeostasis.