Article

Overexpression of IGF-1 in Muscle Attenuates Disease in a Mouse Model of Spinal and Bulbar Muscular Atrophy

Neurogenetics Branch, NINDS, NIH, Bethesda, MD 20892, USA.
Neuron (Impact Factor: 15.98). 09/2009; 63(3):316-28. DOI: 10.1016/j.neuron.2009.07.019
Source: PubMed

ABSTRACT Expansion of a polyglutamine tract in the androgen receptor (AR) causes spinal and bulbar muscular atrophy (SBMA). We previously showed that Akt-mediated phosphorylation of AR reduces ligand binding and attenuates the mutant AR toxicity. Here, we show that in culture insulin-like growth factor 1 (IGF-1) reduces AR aggregation and increases AR clearance via the ubiquitin-proteasome system through phosphorylation of AR by Akt. In vivo, SBMA transgenic mice overexpressing a muscle-specific isoform of IGF-1 selectively in skeletal muscle show evidence of increased Akt activation and AR phosphorylation and decreased AR aggregation. Augmentation of IGF-1/Akt signaling rescues behavioral and histopathological abnormalities, extends the life span, and reduces both muscle and spinal cord pathology of SBMA mice. This study establishes IGF-1/Akt-mediated inactivation of mutant AR as a strategy to counteract disease in vivo and demonstrates that skeletal muscle is a viable target tissue for therapeutic intervention in SBMA.

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Available from: Maria Pennuto, Aug 26, 2015
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    • "Furthermore, there is also no reduction in the number of cultured motor neurons maintained in DHT for 10 days after dissociation in the other patient cultures. This finding is consistent with analysis of motor neuron counts from the spinal cord of SBMA model mice which do not show a significant reduction of motor neuron numbers (Katsuno et al., 2002; Palazzolo et al., 2009). The finding that control and SBMA motor neuron cultures have well developed processes that stain for SMI-32, β-tubulin, and neurofilament suggests that the differentiation potential of the SBMA motor neuron cells is intact. "
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    ABSTRACT: Spinal and bulbar muscular atrophy (SBMA, Kennedy's disease), is a motor neuron disease caused by polyglutamine repeat expansion in the androgen receptor. Although degeneration occurs in the spinal cord and muscle, the exact mechanism is not clear. Induced pluripotent stem cells from spinal and bulbar muscular atrophy patients provide a useful model for understanding the disease mechanism and designing effective therapy. Stem cells were generated from six patients and compared to control lines from three healthy individuals. Motor neurons from four patients were differentiated from stem cells and characterized to understand disease-relevant phenotypes. Stem cells created from patient fibroblasts express less androgen receptor than control cells, but show androgen-dependent stabilization and nuclear translocation. The expanded repeat in several stem cell clones was unstable, with either expansion or contraction. Patient stem cell clones produced a similar number of motor neurons compared to controls, with or without androgen treatment. The stem cell-derived motor neurons had immunoreactivity for HB9, Isl1, ChAT, and SMI-32, and those with the largest repeat expansions were found to have increased acetylated α-tubulin and reduced HDAC6. Reduced HDAC6 was also found in motor neuron cultures from two other patients with shorter repeats. Evaluation of stably transfected mouse cells and SBMA spinal cord showed similar changes in acetylated α-tubulin and HDAC6. Perinuclear lysosomal enrichment, an HDAC6 dependent process, was disrupted in motor neurons from two patients with the longest repeats. SBMA stem cells present new insights into the disease, and the observations of reduced androgen receptor levels, repeat instability, and reduced HDAC6 provide avenues for further investigation of the disease mechanism and development of effective therapy.
    Neurobiology of Disease 06/2014; 70. DOI:10.1016/j.nbd.2014.05.038 · 5.20 Impact Factor
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    • "Supporting a role for muscle in pathogenesis are data from transgenic mice that overexpress wild-type (WT) AR only in skeletal muscle and show hormonedependent myopathy and motor axon loss (Johansen et al., 2009; Monks et al., 2007). That muscle both contributes to the SBMA phenotype and provides a therapeutic target is supported by data showing diminished disease severity in polyQ-AR transgenic mice with genetic overexpression of IGF-1 in skeletal muscle (Palazzolo et al., 2009) or with peripheral IGF-1 administration (Rinaldi et al., 2012). Here, we test an alternative strategy to ameliorate toxicity in mouse models of SBMA by suppressing polyQ-AR expression using antisense oligonucleotides (ASOs). "
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    ABSTRACT: Spinal and bulbar muscular atrophy (SBMA) is caused by the polyglutamine androgen receptor (polyQ-AR), a protein expressed by both lower motor neurons and skeletal muscle. Although viewed as a motor neuronopathy, data from patients and mouse models suggest that muscle contributes to disease pathogenesis. Here, we tested this hypothesis using AR113Q knockin and human bacterial artificial chromosome/clone (BAC) transgenic mice that express the full-length polyQ-AR and display androgen-dependent weakness, muscle atrophy, and early death. We developed antisense oligonucleotides that suppressed AR gene expression in the periphery but not the CNS after subcutaneous administration. Suppression of polyQ-AR in the periphery rescued deficits in muscle weight, fiber size, and grip strength, reversed changes in muscle gene expression, and extended the lifespan of mutant males. We conclude that polyQ-AR expression in the periphery is an important contributor to pathology in SBMA mice and that peripheral administration of therapeutics should be explored for SBMA patients.
    Cell Reports 04/2014; 7(3). DOI:10.1016/j.celrep.2014.02.008 · 8.36 Impact Factor
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    • "Insulin-like growth factor 1 (IGF-1) stimulation increased the survival rate of the MN-1 cells stably expressing AR65Q through the phospho-inositol-3-kinase (PI3K) pathway and activation of Akt. IGF-1/Akt signaling also reduced polyQ AR aggregation and increased polyQ AR degradation by the UPS in a phosphorylationdependent manner (Palazzolo et al., 2009). To study the effects of IGF-1 in vivo, transgenic AR97Q mice were crossed with mice overexpressing a rat, non-circulating, muscle-specific isoform of IGF-1. "
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    ABSTRACT: Spinal and bulbar muscular atrophy (SBMA, Kennedy's disease), a late-onset neuromuscular disorder, is caused by expansion of the polymorphic polyglutamine tract in the androgen receptor (AR). The AR is a ligand-activated transcription factor, but plays roles in other cellular pathways. In SBMA, selective motor neuron degeneration occurs in the brainstem and spinal cord, thus the causes of neuronal dysfunction have been studied. However, pathogenic pathways in muscles may also be involved. Cultured cells, fly and mouse models are used to study the molecular mechanisms leading to SBMA. Both the structure of the polyglutamine-expanded AR (polyQ AR) and its interactions with other proteins are altered relative to the normal AR. The ligand-dependent translocation of the polyQ AR to the nucleus appears to be critical, as are interdomain interactions. The polyQ AR, or fragments thereof, can form nuclear inclusions, but their pathogenic or protective nature is unclear. Other data suggests soluble polyQ AR oligomers can be harmful. Post-translational modifications such as phosphorylation, acetylation, and ubiquitination influence AR function and modulate the deleterious effects of the polyQ AR. Transcriptional dysregulation is highly likely to be a factor in SBMA; deregulation of non-genomic AR signaling may also be involved. Studies on polyQ AR-protein degradation suggest inhibition of the ubiquitin proteasome system and changes to autophagic pathways may be relevant. Mitochondrial function and axonal transport may also be affected by the polyQ AR. Androgens, acting through the AR, can be neurotrophic and are important in muscle development; hence both loss of normal AR functions and gain of novel harmful functions by the polyQ AR can contribute to neurodegeneration and muscular atrophy. Thus investigations into polyQ AR function have shown that multiple complex mechanisms lead to the initiation and progression of SBMA.
    Frontiers in Neurology 05/2013; 4:53. DOI:10.3389/fneur.2013.00053
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