Progressive abnormalities in skeletal muscle and neuromuscular junctions of transgenic mice expressing the Huntington's disease mutation. Eur J Neurosci

University of Cambridge, Cambridge, England, United Kingdom
European Journal of Neuroscience (Impact Factor: 3.18). 01/2005; 20(11):3092-114. DOI: 10.1111/j.1460-9568.2004.03783.x
Source: PubMed


Huntington's disease (HD) is a neurodegenerative disorder with complex symptoms dominated by progressive motor dysfunction. Skeletal muscle atrophy is common in HD patients. Because the HD mutation is expressed in skeletal muscle as well as brain, we wondered whether the muscle changes arise from primary pathology. We used R6/2 transgenic mice for our studies. Unlike denervation atrophy, skeletal muscle atrophy in R6/2 mice occurs uniformly. Paradoxically however, skeletal muscles show age-dependent denervation-like abnormalities, including supersensitivity to acetylcholine, decreased sensitivity to mu-conotoxin, and anode-break action potentials. Morphological abnormalities of neuromuscular junctions are also present, particularly in older R6/2 mice. Severely affected R6/2 mice show a progressive increase in the number of motor endplates that fail to respond to nerve stimulation. Surprisingly, there was no constitutive sprouting of motor neurons in R6/2 muscles, even in severely atrophic muscles that showed other denervation-like characteristics. In fact, there was an age-dependent loss of regenerative capacity of motor neurons in R6/2 mice. Because muscle fibers appear to be released from the activity-dependent cues that regulate membrane properties and muscle size, and motor axons and nerve terminals become impaired in their capacity to release neurotransmitter and to respond to stimuli that normally evoke sprouting and adaptive reinnervation, we speculate that in these mice there is a progressive dissociation of trophic signalling between motor neurons and skeletal muscle. However, irrespective of the cause, the abnormalities at neuromuscular junctions we report here are likely to contribute to the pathological phenotype in R6/2 mice, particularly in late stages of the disease.

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Available from: Thomas M Wishart
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    • "Weakness and wasting of muscle have been reported both in patients and in animal models of HD (Djoussé et al., 2002; Hamilton et al., 2004; Gizatullina et al., 2006; Kosinski et al., 2007; Turner et al., 2007; Busse et al., 2008). Functional measurements in living muscle fibers are only available for the R6/2 mouse model and demonstrated alterations in membrane properties and excitability (Ribchester et al., 2004). R6/2 was originally "
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    ABSTRACT: Huntington's disease (HD) is caused by an expanded CAG trinucleotide repeat within the gene encoding the protein huntingtin. The resulting elongated glutamine (poly-Q) sequence of mutant huntingtin (mhtt) affects both central neurons and skeletal muscle. Recent reports suggest that ryanodine receptor-based Ca(2+) signaling, which is crucial for skeletal muscle excitation-contraction coupling (ECC), is changed by mhtt in HD neurons. Consequently, we searched for alterations of ECC in muscle fibers of the R6/2 mouse, a mouse model of HD. We performed fluorometric recordings of action potentials (APs) and cellular Ca(2+) transients on intact isolated toe muscle fibers (musculi interossei), and measured L-type Ca(2+) inward currents on internally dialyzed fibers under voltage-clamp conditions. Both APs and AP-triggered Ca(2+) transients showed slower kinetics in R6/2 fibers than in fibers from wild-type mice. Ca(2+) removal from the myoplasm and Ca(2+) release flux from the sarcoplasmic reticulum were characterized using a Ca(2+) binding and transport model, which indicated a significant reduction in slow Ca(2+) removal activity and Ca(2+) release flux both after APs and under voltage-clamp conditions. In addition, the voltage-clamp experiments showed a highly significant decrease in L-type Ca(2+) channel conductance. These results indicate profound changes of Ca(2+) turnover in skeletal muscle of R6/2 mice and suggest that these changes may be associated with muscle pathology in HD.
    Full-text · Article · Nov 2014 · The Journal of General Physiology
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    • "Numerous behavioral and neurological symptoms similar to what seen in HD patients have been also observed in transgenic mouse models [11,12] including those expressing only short fragments of mut-HTT, as R6/2 mice [13]. R6/2 is one of the first HD transgenic mouse model created, expressing only the N-terminal fragment of HTT (exon 1) and it is characterized by short survival and development of pathological features mimicking human stages of disease [13,14]. For this reason, transcriptional and behavioral alterations have been intensely studied in R6/2, which has being commonly employed not only in pre-clinical drug testing but also in peripheral investigations, often realized in parallel with HD patients [15,16]. "
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    ABSTRACT: Huntington Disease (HD) is a progressive neurological disorder, with pathological manifestations in brain areas and in periphery caused by the ubiquitous expression of mutant Huntingtin protein. Transcriptional dysregulation is considered a key molecular mechanism responsible of HD pathogenesis but, although numerous studies investigated mRNA alterations in HD, so far none evaluated a whole gene expression profile in blood of R6/2 mouse model. To discover novel pathogenic mechanisms and potential peripheral biomarkers useful to monitor disease progression or drug efficacy, a microarray study was performed in blood of R6/2 at manifest stage and wild type littermate mice. This approach allowed to propose new peripheral molecular processes involved in HD and to suggest different panels of candidate biomarkers. Among the discovered deregulated processes, we focused on specific ones: complement and coagulation cascades, PPAR signaling, cardiac muscle contraction, and dilated cardiomyopathy pathways. Selected genes derived from these pathways were additionally investigated in other accessible tissues to validate these matrices as source of biomarkers, and in brain, to link central and peripheral disease manifestations. Our findings validated the skeletal muscle as suitable source to investigate peripheral transcriptional alterations in HD and supported the hypothesis that immunological alteration may contribute to neurological degeneration. Moreover, the identification of altered signaling in mouse blood enforce R6/2 transgenic mouse as a powerful HD model while suggesting novel disease biomarkers for pre-clinical investigation.
    Full-text · Article · Oct 2013
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    • "Mutant huntingtin is expressed in nearly all tissues, including the GI tract, and has been shown to form aggregates in the enteric nervous system of HD mouse models (Moffitt et al., 2009; Sathasivam et al., 1999). HD patients suffer from several problems, including progressive weight loss (Djousse et al., 2002; Farrer and Yu, 1985; Robbins et al., 2006; Sanberg et al., 1981), nutritional deficiencies (Lanska et al., 1988), swallowing difficulties (Wood et al., 2008), gastritis and esophagitis (Andrich et al., 2009), decreased bone density (Bonelli et al., 2002; Goodman and Barker, 2011), and muscular atrophy (Ribchester et al., 2004), that could be related to dysfunction of the digestive tract. Here we report that the GI tract is affected in R6/2 mice. "
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    ABSTRACT: Weight loss is the most important non-neurological complication of Huntington's disease (HD). It correlates with disease progression and affects the quality of life of HD patients, suggesting that it could be a valuable target for therapeutic intervention. The mechanism underlying weight loss in HD is unknown. Mutant huntingtin, the protein that causes the disease, is not only expressed in the brain, but also along the gastrointestinal (GI) tract. Here we demonstrate that the GI tract of HD mice is affected. At the anatomical level we observed loss of enteric neuropeptides, as well as decreased mucosal thickness and villus length. Exploring the functions of the GI system we found impaired gut motility, diarrhea, and malabsorption of food. The degree of malabsorption was inversely associated with body weight, suggesting that GI dysfunction plays an important role in weight loss in HD mice. In summary, these observations suggest that the GI tract is affected in HD mice and that GI dysfunction contributes to nutritional deficiencies and weight loss.
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