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)

Reduced number of axonal mitochondria and tau hypophosphorylation in mouse P301L tau knockin neurons.

Expression of the frontotemporal dementia-related tau mutation, P301L, at physiological levels in adult mouse brain (KI-P301L mice) results in overt hypophosphorylation of tau and age-dependent alterations in axonal mitochondrial transport in peripheral nerves. To determine the effects of P301L tau expression in the central nervous system, we examined the kinetics of mitochondrial axonal transport and tau phosphorylation in primary cortical neurons from P301L knock-in (KI-P301L) mice. We observed a significant 50% reduction in the number of mitochondria in the axons of cortical neurons cultured from KI-P301L mice compared to wild-type neurons. Expression of murine P301L tau did not change the speed, direction of travel or likelihood of movement of mitochondria. Notably, the angle that defines the orientation of the mitochondria in the axon, and the volume of individual moving mitochondria, were significantly increased in neurons expressing P301L tau. We found that murine tau phosphorylation in KI-P301L mouse neurons was diminished and the ability of P301L tau to bind to microtubules was also reduced compared to tau in wild-type neurons. The P301L mutation did not influence the ability of murine tau to associate with membranes in cortical neurons or in adult mouse brain. We conclude that P301L tau is associated with mitochondrial changes and causes an early reduction in murine tau phosphorylation in neurons coupled with impaired microtubule binding of tau. These results support the association of mutant tau with detrimental effects on mitochondria and will be of significance for the pathogenesis of tauopathies

Loss of TMEM106B exacerbates C9ALS/FTD DPR pathology by disrupting autophagosome maturation

Disruption to protein homeostasis caused by lysosomal dysfunction and associated impairment of autophagy is a prominent pathology in amyotrophic lateral sclerosis and frontotemporal dementia (ALS/FTD). The most common genetic cause of ALS/FTD is a G4C2 hexanucleotide repeat expansion in C9orf72 (C9ALS/FTD). Repeat-associated non-AUG (RAN) translation of G4C2 repeat transcripts gives rise to dipeptide repeat (DPR) proteins that have been shown to be toxic and may contribute to disease etiology. Genetic variants in TMEM106B have been associated with frontotemporal lobar degeneration with TDP-43 pathology and disease progression in C9ALS/FTD. TMEM106B encodes a lysosomal transmembrane protein of unknown function that is involved in various aspects of lysosomal biology. How TMEM106B variants affect C9ALS/FTD is not well understood but has been linked to changes in TMEM106B protein levels. Here, we investigated TMEM106B function in the context of C9ALS/FTD DPR pathology. We report that knockdown of TMEM106B expression exacerbates the accumulation of C9ALS/FTD-associated cytotoxic DPR proteins in cell models expressing RAN-translated or AUG-driven DPRs as well as in C9ALS/FTD-derived iAstrocytes with an endogenous G4C2 expansion by impairing autophagy. Loss of TMEM106B caused a block late in autophagy by disrupting autophagosome to autolysosome maturation which coincided with impaired lysosomal acidification, reduced cathepsin activity, and juxtanuclear clustering of lysosomes. Lysosomal clustering required Rab7A and coincided with reduced Arl8b-mediated anterograde transport of lysosomes to the cell periphery. Increasing Arl8b activity in TMEM106B-deficient cells not only restored the distribution of lysosomes, but also fully rescued autophagy and DPR protein accumulation. Thus, we identified a novel function of TMEM106B in autophagosome maturation via Arl8b. Our findings indicate that TMEM106B variants may modify C9ALS/FTD by regulating autophagic clearance of DPR proteins. Caution should therefore be taken when considering modifying TMEM106B expression levels as a therapeutic approach in ALS/FTD

C9ORF72 hexanucleotide repeat exerts toxicity in a stable, inducible motor neuronal cell model, which is rescued by partial depletion of Pten.

Amyotrophic lateral sclerosis (ALS) is a devastating and incurable neurodegenerative disease, characterised by progressive failure of the neuromuscular system. A (G4C2)n repeat expansion in C9ORF72 is the most common genetic cause of ALS and frontotemporal dementia (FTD). To date, the balance of evidence indicates that the (G4C2)n repeat causes toxicity and neurodegeneration via a gain-of-toxic function mechanism; either through direct RNA toxicity or through the production of toxic aggregating dipeptide repeat proteins. Here, we have generated a stable and isogenic motor neuronal NSC34 cell model with inducible expression of a (G4C2)102 repeat, to investigate the gain-of-toxic function mechanisms. The expression of the (G4C2)102 repeat produces RNA foci and also undergoes RAN translation. In addition, the expression of the (G4C2)102 repeat shows cellular toxicity. Through comparison of transcriptomic data from the cellular model with laser-captured spinal motor neurons from C9ORF72-ALS cases, we also demonstrate that the PI3K/Akt cell survival signalling pathway is dysregulated in both systems. Furthermore, partial knockdown of Pten rescues the toxicity observed in the NSC34 (G4C2)102 cellular gain-of-toxic function model of C9ORF72-ALS. Our data indicate that PTEN may provide a potential therapeutic target to ameliorate toxic effects of the (G4C2)n repeat

Performance of the CMS Cathode Strip Chambers with Cosmic Rays

The Cathode Strip Chambers (CSCs) constitute the primary muon tracking device in the CMS endcaps. Their performance has been evaluated using data taken during a cosmic ray run in fall 2008. Measured noise levels are low, with the number of noisy channels well below 1%. Coordinate resolution was measured for all types of chambers, and fall in the range 47 microns to 243 microns. The efficiencies for local charged track triggers, for hit and for segments reconstruction were measured, and are above 99%. The timing resolution per layer is approximately 5 ns

A comparison of in vitro properties of resting SOD1 transgenic microglia reveals evidence of reduced neuroprotective function

<p>Abstract</p> <p>Background</p> <p>Overexpression of mutant copper/zinc superoxide dismutase (<it>SOD1</it>) in rodents has provided useful models for studying the pathogenesis of amyotrophic lateral sclerosis (ALS). Microglia have been shown to contribute to ALS disease progression in these models, although the mechanism of this contribution remains to be elucidated. Here, we present the first evidence of the effects of overexpression of mutant (TG G93A) and wild type (TG WT) human <it>SOD1 </it>transgenes on a set of functional properties of microglia relevant to ALS progression, including expression of integrin β-1, spreading and migration, phagocytosis of apoptotic neuronal cell debris, and intracellular calcium changes in response to an inflammatory stimulus.</p> <p>Results</p> <p>TG SOD1 G93A but not TG SOD1 WT microglia had lower expression levels of the cell adhesion molecule subunit integrin β-1 than their NTG control cells [NTG (G93A) and NTG (WT), respectively, 92.8 ± 2.8% on TG G93A, 92.0 ± 6.6% on TG WT, 100.0 ± 1.6% on NTG (G93A), and 100.0 ± 2.7% on NTG (WT) cells], resulting in decreased spreading ability, with no effect on ability to migrate. Both TG G93A and TG WT microglia had reduced capacity to phagocytose apoptotic neuronal cell debris (13.0 ± 1.3% for TG G93A, 16.5 ± 1.9% for TG WT, 28.6 ± 1.8% for NTG (G93A), and 26.9 ± 2.8% for NTG (WT) cells). Extracellular stimulation of microglia with ATP resulted in smaller increase in intracellular free calcium in TG G93A and TG WT microglia relative to NTG controls (0.28 ± 0.02 μM for TG G93A, 0.24 ± 0.03 μM for TG WT, 0.39 ± 0.03 μM for NTG (G93A), and 0.37 ± 0.05 μM for NTG (WT) microglia).</p> <p>Conclusions</p> <p>These findings indicate that, under resting conditions, microglia from mutant <it>SOD1 </it>transgenic mice have a reduced capacity to elicit physiological responses following tissue disturbances and that higher levels of stimulatory signals, and/or prolonged stimulation may be necessary to initiate these responses. Overall, resting mutant <it>SOD1</it>-overexpressing microglia may have reduced capacity to function as sensors of disturbed tissue/cellular homeostasis in the CNS and thus have reduced neuroprotective function.</p

SRSF1-dependent nuclear export inhibition of C9ORF72 repeat transcripts prevents neurodegeneration and associated motor deficits.

Hexanucleotide repeat expansions in the C9ORF72 gene are the commonest known genetic cause of amyotrophic lateral sclerosis and frontotemporal dementia. Expression of repeat transcripts and dipeptide repeat proteins trigger multiple mechanisms of neurotoxicity. How repeat transcripts get exported from the nucleus is unknown. Here, we show that depletion of the nuclear export adaptor SRSF1 prevents neurodegeneration and locomotor deficits in a Drosophila model of C9ORF72-related disease. This intervention suppresses cell death of patient-derived motor neuron and astrocytic-mediated neurotoxicity in co-culture assays. We further demonstrate that either depleting SRSF1 or preventing its interaction with NXF1 specifically inhibits the nuclear export of pathological C9ORF72 transcripts, the production of dipeptide-repeat proteins and alleviates neurotoxicity in Drosophila, patient-derived neurons and neuronal cell models. Taken together, we show that repeat RNA-sequestration of SRSF1 triggers the NXF1-dependent nuclear export of C9ORF72 transcripts retaining expanded hexanucleotide repeats and reveal a novel promising therapeutic target for neuroprotection.MRC, ERC, FP

A distinct role for B1b lymphocytes in T cell-independent immunity

Pathogenesis of infectious disease is not only determined by the virulence of the microbe but also by the immune status of the host. Vaccination is the most effective means to control infectious diseases. A hallmark of the adaptive immune system is the generation of B cell memory, which provides a long-lasting protective antibody response that is central to the concept of vaccination. Recent studies revealed a distinct function for B1b lymphocytes, a minor subset of mature B cells that closely resembles that of memory B cells in a number of aspects. In contrast to the development of conventional B cell memory, which requires the formation of germinal centers and T cells, the development of B1b cell-mediated long-lasting antibody responses occurs independent of T cell help. T cell-independent (TI) antigens are important virulence factors expressed by a number of bacterial pathogens, including those associated with biological threats. TI antigens cannot be processed and presented to T cells and therefore are known to possess restricted T cell-dependent (TD) immunogenicity. Nevertheless, specific recognition of TI antigens by B1b cells and the highly protective antibody responses mounted by them clearly indicate a crucial role for this subset of B cells. Understanding the mechanisms of long-term immunity conferred by B1b cells may lead to improved vaccine efficacy for a variety of TI antigens

CMS physics technical design report : Addendum on high density QCD with heavy ions

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