Article

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

ABSTRACT

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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    • "There were no changes in Beclin 1 and Atg12-Atg5, but there were significant increases in LC3-II, p62, Lamp2, and Cathepsin D already at 150 days, i.e. before onset of symptoms, and further increases at the symptomatic and terminal stages. This is similar to what has been found in other ALS models[25,56]. In humans, there were also increases in Beclin-1 and Atg12-Atg5, but not LC3-II, suggesting the existence of some species differences in the autophagic response to SOD1-provoked ALS (Fig. 2c–f). "
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    ABSTRACT: The motor system is selectively vulnerable to mutations in the ubiquitously expressed aggregation-prone enzyme superoxide dismutase-1 (SOD1). Autophagy clears aggregates, and factors involved in the process were analyzed in multiple areas of the CNS from human control subjects (n = 10) and amyotrophic lateral sclerosis (ALS) patients (n = 18) with or without SOD1 mutations. In control subjects, the key regulatory protein Beclin 1 and downstream factors were remarkably scarce in spinal motor areas. In ALS patients, there was evidence of moderate autophagy activation and also dysregulation. These changes were largest in SOD1 mutation carriers. To explore consequences of low autophagy capacity, effects of a heterozygous deletion of Beclin 1 were examined in ALS mouse models expressing mutant SOD1s. This caused earlier SOD1 aggregation, onset of symptoms, motor neuron loss, and a markedly shortened survival. In contrast, the levels of soluble misfolded SOD1 species were reduced. The findings suggest that an inherent low autophagy capacity might cause the vulnerability of the motor system, and that SOD1 aggregation plays a crucial role in the pathogenesis.
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    • "However, complete inhibition of mTOR by high concentrations of rapamycin has detrimental effects on long-term memory facilitation and consolidation , and causes amnesia (Bove et al., 2011; Tischmeyer et al., 2003). In addition, rapamycin treatment in mutant superoxide dismutase 1 (SOD1) mice exacerbates ALS pathology (Zhang et al., 2011). Therefore, rapamycin may act as a neuroprotective agent for fighting neurodegenerative diseases, but some attentions should be paid not only to the dosage of rapamycin but also to the mutations of some genes (e.g. "
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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.
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