Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease affecting motor neurons. Disease onset and progression are variable, with survival ranging from months to decades. Factors underlying this variability may represent targets for therapeutic intervention. Here, we have screened a zebrafish model of ALS and identified Epha4, a receptor in the ephrin axonal repellent system, as a modifier of the disease phenotype in fish, rodents and humans. Genetic as well as pharmacological inhibition of Epha4 signaling rescues the mutant SOD1 phenotype in zebrafish and increases survival in mouse and rat models of ALS. Motor neurons that are most vulnerable to degeneration in ALS express higher levels of Epha4, and neuromuscular re-innervation by axotomized motor neurons is inhibited by the presence of Epha4. In humans with ALS, EPHA4 expression inversely correlates with disease onset and survival, and loss-of-function mutations in EPHA4 are associated with long survival. Furthermore, we found that knockdown of Epha4 also rescues the axonopathy induced by expression of mutant TAR DNA-binding protein 43 (TDP-43), another protein causing familial ALS, and the axonopathy induced by knockdown of survival of motor neuron 1, a model for spinomuscular atrophy. This suggests that Epha4 generically modulates the vulnerability of (motor) neurons to axonal degeneration and may represent a new target for therapeutic intervention.

Regular treatment of patients with mild asthma with salmeterol leads to tolerance to its protective effects against a bronchoconstrictor stimulus, in this case inhaled methacholine, despite well-maintained bronchodilation. This finding raises concern about the effectiveness of prolonged therapy with long-acting beta 2-adrenoceptor agonists in asthma.

We conclude that the severity of cold, as induced by experimental RV16 infection, is a determinant of the increase in airway hypersensitivity to histamine in patients with asthma. Our results suggest that this may be mediated by an inflammatory mechanism, involving the release of chemokines such as IL-8.

Exacerbations of asthma are often associated with respiratory infections, and particularly those caused by rhinovirus. The causative role of rhinovirus in these acute episodes is still unclear, since it has not been determined whether or not infection with the virus promotes excessive airway narrowing in asthma. We tested the hypothesis that experimental infection with inhaled wild-type rhinovirus 16 (RV16) increases the maximal degree of airway narrowing in response to bronchoconstrictor stimuli in patients with mild to moderate asthma. Fourteen nonsmoking subjects with atopic asthma and normal FEV1 values participated in a double-blind, placebo-controlled, parallel study. A total dose of 3 x 10(4) of the 50% tissue-culture-infective dose (TCID50) of RV16 or a placebo was administered by pipette, atomizer, and nebulizer in equal doses into both nostrils on two consecutive days. Dose-response curves for inhaled methacholine were recorded 1 d before and 2, 7, and 15 d after RV16 infection or placebo. The response to methacholine was measured by the percent decrease in FEV1, and the maximal degree of airway narrowing was expressed by the average response on the plateau of the dose-response curve. In the seven subjects receiving the virus, RV16 infection was confirmed in nasal washings and/or by an increase in antibody titer, whereas these tests were negative in the placebo group. There was no significant change in baseline FEV1 during the study in either group (p = 0.06).(ABSTRACT TRUNCATED AT 250 WORDS)

Mislocalization, aberrant processing and aggregation of TAR DNA-binding protein 43 (TDP-43) is found in the neurons affected by two related diseases, amyotrophic lateral sclerosis (ALS) and frontotemporal lobe dementia (FTLD). These TDP-43 abnormalities are seen when TDP-43 is mutated, such as in familial ALS, but also in FTLD, caused by null mutations in the progranulin gene. They are also found in many patients with sporadic ALS and FTLD, conditions in which only wild type TDP-43 is present. The common pathological hallmarks and symptomatic cross over between the two diseases suggest that TDP-43 and progranulin may be mechanistically linked. In this study we aimed to address this link by establishing whether overexpression of mutant TDP-43 or knock-down of progranulin in zebrafish embryos results in motor neuron phenotypes and whether human progranulin is neuroprotective against such phenotypes. Mutant TDP-43 (A315T mutation) induced a motor axonopathy characterized by short axonal outgrowth and aberrant branching, similar, but more severe, than that induced by mutant SOD1. Knockdown of the two zebrafish progranulin genes, grna and grnb, produced a substantial decrease in axonal length, with knockdown of grna alone producing a greater decrease in axonal length than grnb. Progranulin overexpression rescued the axonopathy induced by progranulin knockdown. Interestingly, progranulin also rescued the mutant TDP-43 induced axonopathy, whilst it failed to affect the mutant SOD1-induced phenotype. TDP-43 was found to be nuclear in all conditions described. The findings described here demonstrate that progranulin is neuroprotective in vivo and may have therapeutic potential for at least some forms of motor neuron degeneration.

The exact mechanism underlying amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) associated with the GGG GCC repeat expansion in C9orf72 is still unclear. Two gain-of-function mechanisms are possible: repeat RNA toxicity and dipeptide repeat protein (DPR) toxicity. We here dissected both possibilities using a zebrafish model for ALS. Expression of two DPRs, glycine-arginine and proline-arginine, induced a motor axonopathy. Similarly, expanded sense and antisense repeat RNA also induced a motor axonopathy and formed mainly cytoplasmic RNA foci. However, DPRs were not detected in these conditions. Moreover, stop codon-interrupted repeat RNA still induced a motor axonopathy and a synergistic role of low levels of DPRs was excluded. Altogether, these results show that repeat RNA toxicity is independent of DPR formation. This RNA toxicity, but not the DPR toxicity, was attenuated by the RNA-binding protein Pur-alpha and the autophagy-related protein p62. Our findings demonstrate that RNA toxicity, independent of DPR toxicity, can contribute to the pathogenesis of C9orf72-associated ALS/FTD.

Defects in axonal transport are thought to contribute to the pathogenesis of neurodegenerative disease. Because α-tubulin acetylation facilitates axonal transport, inhibition of the α-tubulin deacetylating enzymes, histone deacetylase 6 (Hdac6) and silent information regulator 2 (Sirt2), is thought to be an interesting therapeutic strategy for these conditions. Amyotrophic lateral sclerosis (ALS) is a one such rapidly progressive and fatal neurodegenerative disorder, in which axonal transport defects have been found in vitro and in vivo. To establish whether the inhibition of Hdac6 or Sirt2 may be of interest for ALS treatment, we investigated whether deleting Hdac6 or Sirt2 from the superoxide dismutase 1, SOD1(G93A) mouse affects the motor neuron degeneration in this ALS model. Deletion of Hdac6 significantly extended the survival of SOD1(G93A) mice without affecting disease onset, and maintained motor axon integrity. This protective effect was associated with increased α-tubulin acetylation. Deletion of Sirt2 failed to affect the disease course, but also did not modify α-tubulin acetylation. These findings show that Hdac6, rather than Sirt2, is a therapeutic target for the treatment of ALS. Moreover, Sirt2 appears not to be a major α-tubulin deacetylase in the nervous system.

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