Comparative transcription map of the wobbler critical region on mouse chromosome 11 and the homologous region on human chromosome 2p13-14

Deregulated miR-29b-3p Correlates with Tissue-Specific Activation of Intrinsic Apoptosis in An Animal Model of Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is one of the most common incurable motor neuron disorders in adults. The majority of all ALS cases occur sporadically (sALS). Symptoms of ALS are caused by a progressive degeneration of motor neurons located in the motor cortex and spinal cord. The question arises why motor neurons selectively degenerate in ALS, while other cells and systems appear to be spared the disease. Members of the intrinsic apoptotic pathway are frequent targets of altered microRNA expression. Therefore, microRNAs and their effects on cell survival are subject of controversial debates. In this study, we investigated the expression of numerous members of the intrinsic apoptotic cascade by qPCR, western blot, and immunostaining in two different regions of the CNS of wobbler mice. Further we addressed the expression of miR-29b-3p targeting BMF, Bax, and, Bak, members of the apoptotic pathway. We show a tissue-specific differential expression of BMF, Bax, and cleaved-Caspase 3 in wobbler mice. An opposing regulation of miR-29b-3p expression in the cerebellum and cervical spinal cord of wobbler mice suggests different mechanisms regulating the intrinsic apoptotic pathway. Based on our findings, it could be speculated that miR-29b-3p might regulate antiapoptotic survival mechanisms in CNS areas that are not affected by neurodegeneration in the wobbler mouse ALS model.

VPS54 and the wobbler mouse

The wobbler mouse is an animal model for human motor neuron disease, such as amyotrophic lateral sclerosis (ALS). The spontaneous, recessive wobbler mutation causes degeneration of upper and lower motor neurons leading to progressive muscle weakness with striking similarities to the ALS pathology. The wobbler mutation is a point mutation affecting Vps54, a component of the Golgi-associated retrograde protein (GARP) complex. The GARP complex is a ubiquitously expressed Golgi-localized vesicle tethering complex, tethering endosome-derived vesicles to the trans Golgi network. The wobbler point mutation leads to a destabilization of the Vps54 protein and thereby the whole GARP complex. This effectuates impairments of the retrograde vesicle transport, mis-sorting of Golgi- and endosome localized proteins and on the long run defects in Golgi morphology and function. It is currently largely unknown how the destabilization of the GARP complex interferes with the pathological hallmarks, reported for the wobbler motor neuron degeneration, like neurofilament aggregation, axonal transport defects, hyperexcitability, mitochondrial dysfunction, and how these finally lead to motor neuron death. However, the impairments of the retrograde vesicle transport and the Golgi-function appear to be critical phenomena in the molecular pathology of the wobbler motor neuron disease.

The wobbler mouse, an ALS animal model

This review article is focused on the research progress made utilizing the wobbler mouse as animal model for human motor neuron diseases, especially the amyotrophic lateral sclerosis (ALS). The wobbler mouse develops progressive degeneration of upper and lower motor neurons and shows striking similarities to ALS. The cellular effects of the wobbler mutation, cellular transport defects, neurofilament aggregation, neuronal hyperexcitability and neuroinflammation closely resemble human ALS. Now, 57 years after the first report on the wobbler mouse we summarize the progress made in understanding the disease mechanism and testing various therapeutic approaches and discuss the relevance of these advances for human ALS. The identification of the causative mutation linking the wobbler mutation to a vesicle transport factor and the research focussed on the cellular basis and the therapeutic treatment of the wobbler motor neuron degeneration has shed new light on the molecular pathology of the disease and might contribute to the understanding the complexity of ALS.

Mutation of Vps54 causes motor neuron disease and defective spermiogenesis in the wobbler mouse

Vacuolar-vesicular protein sorting (Vps) factors are involved in vesicular trafficking in eukaryotic cells. We identified the missense mutation L967Q in Vps54 in the wobbler mouse, an animal model of amyotrophic lateral sclerosis, and also characterized a lethal allele, Vps54(beta-geo). Motoneuron survival and spermiogenesis are severely compromised in the wobbler mouse, indicating that Vps54 has an essential role in these processes.

Inherited motor neuron disease in domestic cats: a model of spinal muscular atrophy

Juvenile-onset spinal muscular atrophy was observed in an extended family of purebred domestic cats as a fully penetrant, simple autosomal recessive trait. Affected kittens exhibited tremor, proximal muscle weakness, and muscle atrophy beginning at ~4 mo of age. Apparent loss of function was rapid initially but progressed slowly after 7-8 mo of age, and variably disabled cats lived for at least 8 y. Electromyography and microscopic examination of muscle and nerve biopsies were consistent with denervation atrophy as a result of a central lesion. There was astrogliosis and dramatic loss of motor neurons in ventral but not dorsal horn gray matter of spinal cord and loss of axons in ventral horn nerve roots. These phenotypic findings were similar to mild forms (type III) of spinal muscular atrophy in humans caused by survival of motor neuron mutations, but molecular analysis excluded feline survival of motor neuron as the disease gene in this family. A breeding colony has been established for further investigation of this naturally occurring large-animal model of inherited motor neuron disease.

Evidence for chronic mitochondrial impairment in the cervical spinal cord of a murine model of motor neuron disease

Profound alteration of the oxygen consumption rate (QO2) is present in the cervical spinal cord (CS) of the wobbler mice aged 12 weeks (wr12). Early symptomatic mice at 4 weeks (wr4) show less pronounced changes with decreases of basal QO2 (P < 0.03) and of QO2 through complex I (P < 0.04). Mitochondrial respiratory enzyme activities, measured spectrophotometrically in the CS homogenate, show no difference between wr12 and controls, whereas complex I is reduced in the wr4 CS (P < 0.0003). Complex I activity is lower than normal both in wr12 and wr4 CS when measured in motor neurons by mean of a histochemical technique. Electron microscopy (EM) reveals a mixture of normal and morphologically altered mitochondria in wr4 motor neurons. The wobbler lumbar spinal cord is spared even at 12 weeks. Our results demonstrate the presence of mitochondrial abnormalities in the wobbler CS since the first manifestations of the disease. Thus, chronic mitochondrial dysfunction has a contributory role in motor neuron degeneration in the wobbler disease.

Brainstem motor nuclei respond differentially to degenerative disease in the mutant mouse wobbler

Degenerative motoneurone diseases, whether in humans, animals, or transgenic mouse models, do not affect all types of motoneurone to the same degree. Understanding the relative differences in vulnerability of certain motor pools may be the key to developing therapies. Expression of calbindin (CB) and parvalbumin (PV) immunoreactivity, which are potentially neuroprotective calcium-binding proteins, and NADPH-diaphorase (NADPH-d) histochemical reactivity, a marker for neurodegeneration, was studied in brainstem sections from mutant wobbler mice and their normal littermates during the motoneurone degeneration phase (3-8 weeks of age). The motor trigeminal and facial nuclei reacted in a manner previously observed in spinal somatic motoneurones in the wobbler. Many motoneurones expressed moderate NADPH-d reactivity, correlated with the appearance of vacuolated motoneurones in Nissl-stained sections. This was not observed in littermate controls. Motoneurone counts from Nissl-stained sections from 14-month-old wobblers and littermates revealed significantly fewer (approximately 27%) motoneurones in the trigeminal nucleus of wobblers. In contrast, the wobbler hypoglossal nucleus contained neither vacuolated nor NADPH-d reactive motoneurones. However, expression of CB immunoreactivity by the majority of wobbler hypoglossal motoneurones was observed but not in littermate controls or in any other motor nucleus. Counts in older animals showed a smaller but still significant difference in motoneurone number between wobblers and controls (approximately 9% reduction). Finally, the wobbler abducens nucleus displayed neither vacuolated neurones, nor NADPH-d reactivity nor CB immunoreactivity. Motor nuclei innervating extraocular muscles appear to be protected in many forms of motoneurone disease in man and other species. However, there were still markedly fewer abducens motoneurones in the old wobblers compared to controls (approximately 29% reduction). Sparing of oculomotor neurones in other diseases has been attributed to their relatively high PV expression, which we also observed in the abducens nucleus of both wobblers and littermates, and to a lesser extent in the other motor nuclei too. In conclusion, our results suggest that, in the wobbler mouse, motoneurone degeneration may occur without overt signs such as cell body vacuolation and NADPH-d expression. Induced CB expression may be neuroprotective but that constitutive expression of PV may not.