Rapamycin treatment augments motor neuron degeneration in SOD1(G93A) mouse model of amyotrophic lateral sclerosis

The Key Laboratory of Stem Cell Biology, Institute of Health Sciences, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences & Shanghai Jiao Tong University School of Medicine, Shanghai, China.
Autophagy (Impact Factor: 11.75). 04/2011; 7(4):412-25. DOI: 10.4161/auto.7.4.14541
Source: PubMed


Aberrant protein misfolding may contribute to the pathogenesis of amyotrophic lateral sclerosis (ALS) but the detailed mechanisms are largely unknown. Our previous study has shown that autophagy is altered in the mouse model of ALS. In the present study, we systematically investigated the correlation of the autophagic alteration with the motor neurons (MNs) degeneration in the ALS mice. We have demonstrated that the autophagic protein marker LC3-II is markedly and specifically increased in the spinal cord MNs of the ALS mice. Electron microscopy and immunochemistry studies have shown that autophagic vacuoles are significantly accumulated in the dystrophic axons of spinal cord MNs of the ALS mice. All these changes in the ALS mice appear at the age of 90 d when the ALS mice display modest clinical symptoms; and they become prominent at the age of 120 d. The clinical symptoms are correlated with the progression of MNs degeneration. Moreover, we have found that p62/SQSTM1 is accumulated progressively in the spinal cord, indicating that the possibility of impaired autophagic flux in the SOD1(G93A) mice. Furthermore, to our surprise, we have found that treatment with autophagy enhancer rapamycin accelerates the MNs degeneration, shortens the life span of the ALS mice, and has no obvious effects on the accumulation of SOD1 aggregates. In addition, we have demonstrated that rapamycin treatment in the ALS mice causes more severe mitochondrial impairment, higher Bax levels and greater caspase-3 activation. These findings suggest that selective degeneration of MNs is associated with the impairment of the autophagy pathway and that rapamycin treatment may exacerbate the pathological processing through apoptosis and other mechanisms in the ALS mice.

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    • "In a nutrient-depleted environment, phosphorylation of mTOR is inhibited, leading to autophagy activation (Diaz-Troya et al. 2008). Thus, a reduced ratio of p-mTOR/mTOR is an indication of autophagy activation (Zhang et al. 2011). We evaluated the protein level of both p-mTOR and mTOR in G93A muscle and found no significant changes in the ratio but a dramatic reduction in the overall mTOR expression level (including pmTOR and mTOR) compared to the wild-type muscle. "
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    ABSTRACT: Accumulation of abnormal protein inclusions is implicated in motor neuron degeneration in amyotrophic lateral sclerosis (ALS). Autophagy, an intracellular process targeting misfolded proteins and damaged organelles for lysosomal degradation, plays crucial roles in survival and diseased conditions. Efforts were made to understand the role of autophagy in motor neuron degeneration and to target autophagy in motor neuron for ALS treatment. However, results were quite contradictory. Possible autophagy defects in other cell types may also complicate the results. Here, we examined autophagy activity in skeletal muscle of an ALS mouse model G93A. Through overexpression of a fluorescent protein LC3-RFP, we found a basal increase in autophagosome formation in G93A muscle during disease progression when the mice were on a regular diet. As expected, an autophagy induction procedure (starvation plus colchicine) enhanced autophagy flux in skeletal muscle of normal mice. However, in response to the same autophagy induction procedure, G93A muscle showed significant reduction in the autophagy flux. Immunoblot analysis revealed that increased cleaved caspase-3 associated with apoptosis was linked to the cleavage of several key proteins involved in autophagy, including Beclin-1, which is an essential molecule connecting autophagy and apoptosis pathways. Taking together, we provide the evidence that the cytoprotective autophagy pathway is suppressed in G93A skeletal muscle and this suppression may link to the enhanced apoptosis during ALS progression. The abnormal autophagy activity in skeletal muscle likely contributes muscle degeneration and disease progression in ALS.
    01/2015; 3(1). DOI:10.14814/phy2.12271
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    • "Different pharmacological approaches to stimulate autophagy have been tested. Two independent studies showed a negative effect on disease progression by treating mouse models of ALS with rapamycin, which is an FDA-approved drug that induces autophagy (Bhattacharya et al., 2012; Zhang et al., 2011). This negative effect was probably due to the immunosuppressive function of rapamycin, as the disease could be slowed down in immunodeficient ALS mice (Staats et al., 2013). "
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    ABSTRACT: Amyotrophic lateral sclerosis (ALS) is characterized by the selective death of motor neurons in the motor cortex, brainstem and spinal cord. It is a neurodegenerative disorder with high genetic and phenotypic variability. In most patients, the cause of the disease is unknown. Until now, no treatment strategy has been discovered with the exception of riluzole which has a moderate effect on the disease process. While developing a new causal therapy targeting a specific disease-causing gene can have a huge effect on the disease process, only a limited number of ALS patients will benefit from such a therapy. Alternatively, pathogenic processes that are common in ALS patients with different etiology can also be targeted. The effect of such a modifying treatment will be smaller, but the target population will be larger as more ALS patients could benefit. In this review, we summarize the evidence for the involvement of different biological processes in the pathogenesis of ALS and will discuss how strategies influencing these processes can be translated into new therapeutic approaches. In order to further improve this translational step, there is an urgent need for a better understanding of the underlying mechanism(s), for new ALS animal models and for rigorous protocols to perform preclinical studies.
    Experimental Neurology 12/2014; 262. DOI:10.1016/j.expneurol.2014.07.001 · 4.70 Impact Factor
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    • "Reduced TOR signaling has been shown in case of VCP mediated ALS (Ching et al., 2013). Feeding SOD1 G93A mutant mice with rapamycin, an inhibitor of TORC1 shortens life span (Zhang et al., 2011). Treating N2A cells expressing mutant TDP-43 with rapamycin has been shown to alter the localization of protein (Caccamo et al., 2009). "
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    ABSTRACT: Amyotrophic Lateral Sclerosis (ALS) is a progressive neurodegenerative disorder characterized by selective death of motor neurons. In 5–10% of the familial cases, the disease is inherited because of mutations. One such mutation, P56S, was identified in human VAPB that behaves in a dominant negative manner, sequestering wild type protein into cytoplasmic inclusions. We have conducted a reverse genetic screen to identify interactors of Drosophila VAPB. We screened 2635 genes and identified 103 interactors, of which 45 were enhancers and 58 were suppressors of VAPB function. Interestingly, the screen identified known ALS loci – TBPH, alsin2 and SOD1. Also identified were genes involved in cellular energetics and homeostasis which were used to build a gene regulatory network of VAPB modifiers. One key modifier identified was Tor, whose knockdown reversed the large bouton phenotype associated with VAP(P58S) expression in neurons. A similar reversal was seen by over-expressing Tuberous Sclerosis Complex (Tsc1,2) that negatively regulates TOR signaling as also by reduction of S6K activity. In comparison, the small bouton phenotype associated with VAP(wt) expression was reversed with Tsc1 knock down as well as S6K-CA expression. Tor therefore interacts with both VAP(wt) and VAP(P58S), but in a contrasting manner. Reversal of VAP(P58S) bouton phenotypes in larvae fed with the TOR inhibitor Rapamycin suggests upregulation of TOR signaling in response to VAP(P58S) expression. The VAPB network and further mechanistic understanding of interactions with key pathways, such as the TOR cassette, will pave the way for a better understanding of the mechanisms of onset and progression of motor neuron disease.
    Biology Open 11/2014; 3(11):1127-38. DOI:10.1242/bio.201410066 · 2.42 Impact Factor
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