Summary A non-coding hexanucleotide repeat expansion in the C9ORF72 gene is the most common mutation associated with familial amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Patients harboring this expansion develop several unique histopathological hallmarks, including intranuclear foci composed of either sense or antisense RNA transcripts from the expanded repeats and dipeptide repeat proteins generated by non-canonical translation of the expanded RNA transcripts. To further investigate the pathological role of C9ORF72 in these diseases, we generated a line of mice carrying a bacterial artificial chromosome containing exons 1 to 6 of the human C9ORF72 gene with approximately 500 repeats of the GGGGCC motif. The mice showed no overt behavioral phenotype but recapitulated distinctive histopathological features that are the hallmark of C9ORF72 ALS/FTD, including sense and antisense intranuclear RNA foci and poly(glycine-proline) dipeptides repeat proteins. Finally, using a synthetic microRNA that targets human C9ORF72 in cultures of primary cortical neurons from the C9BAC mice, we have attenuated expression of the C9BAC transgene and the poly(GP) dipeptides. The C9ORF72 BAC transgenic mice will be a valuable tool in the study of ALS/FTD pathobiology and therapy.

Amyotrophic lateral sclerosis-frontotemporal dementia (ALS-FTD) constitutes a devastating disease spectrum characterised by TDP-43 pathology. Understanding how TDP-43 contributes to neurodegeneration will help direct therapeutic efforts. Here, we have created a novel TDP-43 knock-in mouse with a human-equivalent mutation in the endogenous mouse Tardbp gene. TDP-43Q331K mice demonstrate cognitive dysfunction and a paucity of parvalbumin interneurons. Critically, TDP-43 autoregulation is perturbed leading to a gain of TDP-43 function, and altered splicing of Mapt, another pivotal dementia gene. Furthermore, a novel approach to stratify transcriptomic data by phenotype in differentially affected mutant mice reveals 471 changes linked with improved behaviour. These changes include downregulation of two known modifiers of neurodegeneration, Atxn2 and Arid4a, and upregulation of myelination and translation genes. With one base change in murine Tardbp, this study identifies TDP-43 misregulation as a pathogenic mechanism that may underpin ALS-FTD, and exploits phenotypic heterogeneity to yield candidate suppressors of neurodegenerative disease.

The synucleins (α, β and γ) are highly homologous proteins thought to play a role in regulating neurotransmission and are found abundantly in presynaptic terminals. To overcome functional overlap between synuclein proteins and to understand their role in presynaptic signalling from mesostriatal dopaminergic neurons, we produced mice lacking all three members of the synuclein family. The effect on the mesostriatal system was assessed in adult (4-14 month old) animals using a combination of behavioural, biochemical, histological and electrochemical techniques. Adult triple synuclein null (TKO) mice displayed no overt phenotype, and no change in the number of midbrain dopaminergic neurons. TKO mice were hyperactive in novel environments and exhibited elevated evoked release of dopamine in the striatum detected with fast-scan cyclic voltammetry. Elevated dopamine release was specific to the dorsal not ventral striatum and was accompanied by a decrease of dopamine tissue content. We confirmed a normal synaptic ultrastructure and a normal abundance of SNARE protein complexes in the dorsal striatum. Treatment of TKO animals with drugs affecting dopamine metabolism revealed normal rate of synthesis, enhanced turnover and reduced presynaptic striatal dopamine stores. Our data uniquely reveal the importance of the synuclein proteins in regulating neurotransmitter release from specific populations of midbrain dopamine neurons through mechanisms which differ from those reported in other neurons. The finding that the complete loss of synucleins leads to changes in dopamine handling by presynaptic terminals specifically in those regions preferentially vulnerable in Parkinson’s disease (PD) may ultimately inform on the selectivity of the disease process.

No abstract

The role of α-synuclein in pathogenesis of familial and idiopathic forms of Parkinson’s disease, and other human disorders known as α-synucleinopathies, is well established. In contrast, the involvement of two other members of the synuclein family, β-synuclein and γ-synuclein, in the development and progression of neurodegeneration is poorly studied. However, there is a growing body of evidence that α-synuclein and β-synuclein have opposite neuropathophysiological effects. Unlike α-synuclein, overexpressed β-synuclein does not cause pathological changes in the nervous system of transgenic mice and even ameliorates the pathology caused by overexpressed α-synuclein. To assess the consequences of excess expression of the third family member, γ-synuclein, on the nervous system we generated transgenic mice expressing high levels of mouse γ-synuclein under control of Thy-1 promoter. These animals develop severe age- and transgene dose-dependent neuropathology, motor deficits and die prematurely. Histopathological changes include aggregation of γ-synuclein, accumulation of various inclusions in neuronal cell bodies and processes, and astrogliosis. These changes are seen throughout the nervous system but are most prominent in the spinal cord where they lead to loss of spinal motor neurons. Our data suggest that down-regulation of small heat shock protein HSPB1 and disintegration of neurofilament network play a role in motor neurons dysfunction and death. These findings demonstrate that γ-synuclein can be involved in neuropathophysiological changes and the death of susceptible neurons suggesting the necessity of further investigations of the potential role of this synuclein in disease.

Background: FUS inclusions are hallmarks of certain neurodegenerative diseases.Results: Expression of a highly aggregate prone FUS variant in transgenic mice causes proteinopathy and severe motor phenotype.Conclusion: Aggregation of FUS is sufficient to recapitulate motor pathology typical for amyotrophic lateral sclerosis.Significance: Understanding the role of protein aggregation in the development of human neurodegenerative diseases is crucial for designing efficient therapeutic approaches.

The recent identification of profilin1 mutations in 25 familial ALS cases has linked altered function of this cytoskeleton-regulating protein to the pathogenesis of motor neuron disease. To investigate the pathological role of mutant profilin1 in motor neuron disease, we generated transgenic lines of mice expressing human profilin1 with a mutation at position 118 (hPFN1 G118V ). One of the mouse lines expressing high levels of mutant human PFN1 protein in the brain and spinal cord exhibited many key clinical and pathological features consistent with human ALS disease. These include loss of lower (ventral horn) and upper motor neurons (corticospinal motor neurons in layer V), mutant profilin1 aggregation, abnormally ubiquitinated proteins, reduced choline acetyltransferase (ChAT) enzyme expression, fragmented mitochondria, glial cell activation, muscle atrophy, weight loss, and reduced survival. Our investigations of actin dynamics and axonal integrity suggest that mutant PFN1 protein is associated with an abnormally low filamentous/globular (F/G)-actin ratio that may be the underlying cause of severe damage to ventral root axons resulting in a Wallerian-like degeneration. These observations indicate that our novel profilin1 mutant mouse line may provide a new ALS model with the opportunity to gain unique perspectives into mechanisms of neurodegeneration that contribute to ALS pathogenesis.

A r t i c l e A m e n d m e n t s2 5 4 8