Complete dissociation of motor neuron death from motor dysfunction by Bax deletion in a mouse model of ALS.
ABSTRACT The death of cranial and spinal motoneurons (MNs) is believed to be an essential component of the pathogenesis of amyotrophic lateral sclerosis (ALS). We tested this hypothesis by crossing Bax-deficient mice with mice expressing mutant superoxide dismutase 1 (SOD1), a transgenic model of familial ALS. Although Bax deletion failed to prevent neuromuscular denervation and mitochondrial vacuolization, MNs were completely rescued from mutant SOD1-mediated death. However, Bax deficiency extended lifespan and delayed the onset of motor dysfunction of SOD1 mutants, suggesting that Bax acts via a mechanism distinct from cell death activation. Consistent with this idea, Bax elimination delayed the onset of neuromuscular denervation, which began long before the activation of cell death proteins in SOD1 mutants. Additionally, we show that denervation preceded accumulation of mutant SOD1 within MNs and astrogliosis in the spinal cord, which are also both delayed in Bax-deficient SOD1 mutants. Interestingly, MNs exhibited mitochondrial abnormalities at the innervated neuromuscular junction at the onset of neuromuscular denervation. Additionally, both MN presynaptic terminals and terminal Schwann cells expressed high levels of mutant SOD1 before MNs withdrew their axons. Together, these data support the idea that clinical symptoms in the SOD1 G93A model of ALS result specifically from damage to the distal motor axon and not from activation of the death pathway, and cast doubt on the utility of anti-apoptotic therapies to combat ALS. Furthermore, they suggest a novel, cell death-independent role for Bax in facilitating mutant SOD1-mediated motor denervation.
- SourceAvailable from: Elizabeth B. Moloney[Show abstract] [Hide abstract]
ABSTRACT: Amyotrophic Lateral Sclerosis (ALS) is being redefined as a distal axonopathy, in that many molecular changes influencing motor neuron degeneration occur at the neuromuscular junction (NMJ) at very early stages of the disease prior to symptom onset. A huge variety of genetic and environmental causes have been associated with ALS, and interestingly, although the cause of the disease can differ, both sporadic and familial forms of ALS show a remarkable similarity in terms of disease progression and clinical manifestation. The NMJ is a highly specialized synapse, allowing for controlled signaling between muscle and nerve necessary for skeletal muscle function. In this review we will evaluate the clinical, animal experimental and cellular/molecular evidence that supports the idea of ALS as a distal axonopathy. We will discuss the early molecular mechanisms that occur at the NMJ, which alter the functional abilities of the NMJ. Specifically, we focus on the role of axon guidance molecules on the stability of the cytoskeleton and how these molecules may directly influence the cells of the NMJ in a way that may initiate or facilitate the dismantling of the neuromuscular synapse in the presymptomatic stages of ALS.Frontiers in Neuroscience 08/2014; 8:252.
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ABSTRACT: Objective Research identified promising therapeutics in cell models of Amyotrophic Lateral Sclerosis (ALS), but there is limited progress translating effective treatments to animal models and patients, and ALS remains a disease with no effective treatment. One explanation stems from an acquired pharmacoresistance driven by the drug efflux transporters P-glycoprotein (P-gp) and breast cancer-resistant protein (BCRP), which we have shown are selectively upregulated at the blood-brain and spinal cord barrier (BBB/BSCB) in ALS mice and patients. Pharmacoresistance is well appreciated in other brain diseases, but overlooked in ALS despite many failures in clinical trials.Methods Here, we prove that a P-gp/BCRP-driven pharmacoresistance limits the bioavailability of ALS therapeutics using riluzole, the only FDA-approved drug for ALS and a substrate of P-gp and BCRP. ALS mice (SOD1-G93A) were treated with riluzole and elacridar, to block P-gp and BCRP, and monitored for survival as well as behavioral and physiological parameters.ResultsWe show that riluzole, which normally is not effective when given at onset of symptoms, is now effective in the ALS mice when administered in combination with the P-gp/BCRP inhibitor elacridar. Chronic elacridar treatment increases riluzole Central nervous system (CNS) penetration, improves behavioral measures, including muscle function, slowing down disease progression, and significantly extending survival.InterpretationOur approach improves riluzole efficacy with treatment beginning at symptom onset. Riluzole will not provide a cure, but enhancing its efficacy postsymptoms by addressing pharmacoresistance demonstrates a proof-of-principle concept to consider when developing new ALS therapeutic strategies. We highlight a novel improved therapeutic approach for ALS and demonstrate that pharmacoresistance can no longer be ignored in ALS.Annals of Clinical and Translational Neurology. 11/2014;
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ABSTRACT: Amyotrophic Lateral Sclerosis (ALS), also known as Lou Gehrig's disease, is a neurodegenerative disorder of motor neurons causing progressive muscle weakness, paralysis, and eventual death from respiratory failure. There is currently no cure or effective treatment for ALS. Besides motor neuron degeneration, ALS is associated with impaired energy metabolism, which is pathophysiologically linked to mitochondrial dysfunction and glutamate excitotoxicity. The Deanna Protocol (DP) is a metabolic therapy that has been reported to alleviate symptoms in patients with ALS. In this study we hypothesized that alternative fuels in the form of TCA cycle intermediates, specifically arginine-alpha-ketoglutarate (AAKG), the main ingredient of the DP, and the ketogenic diet (KD), would increase motor function and survival in a mouse model of ALS (SOD1-G93A). ALS mice were fed standard rodent diet (SD), KD, or either diets containing a metabolic therapy of the primary ingredients of the DP consisting of AAKG, gamma-aminobutyric acid, Coenzyme Q10, and medium chain triglyceride high in caprylic triglyceride. Assessment of ALS-like pathology was performed using a pre-defined criteria for neurological score, accelerated rotarod test, paw grip endurance test, and grip strength test. Blood glucose, blood beta-hydroxybutyrate, and body weight were also monitored. SD+DP-fed mice exhibited improved neurological score from age 116 to 136 days compared to control mice. KD-fed mice exhibited better motor performance on all motor function tests at 15 and 16 weeks of age compared to controls. SD+DP and KD+DP therapies significantly extended survival time of SOD1-G93A mice by 7.5% (p = 0.001) and 4.2% (p = 0.006), respectively. Sixty-three percent of mice in the KD+DP and 72.7% of the SD+DP group lived past 125 days, while only 9% of the control animals survived past that point. Targeting energy metabolism with metabolic therapy produces a therapeutic effect in ALS mice which may prolong survival and quality of life in ALS patients.PLoS ONE 07/2014; 9(7):e103526. · 3.53 Impact Factor