Lack of caspase-dependent apoptosis in spinal motor neurons of the wobbler mouse

Neuroprotective effects of the Sigma-1 receptor (S1R) agonist PRE-084, in a mouse model of motor neuron disease not linked to SOD1 mutation

The identification of novel molecular targets crucially involved in motor neuron degeneration/survival is a necessary step for the development of hopefully more effective therapeutic strategies for amyotrophic lateral sclerosis (ALS) patients. In this view, S1R, an endoplasmic reticulum (ER)-resident receptor with chaperone-like activity, has recently attracted great interest. S1R is involved in several processes leading to acute and chronic neurodegeneration, including ALS pathology. Treatment with the S1R agonist PRE-084 improves locomotor function and motor neuron survival in presymptomatic and early symptomatic mutant SOD1-G93A ALS mice. Here, we tested the efficacy of PRE-084 in a model of spontaneous motor neuron degeneration, the wobbler mouse (wr) as a proof of concept that S1R may be regarded as a key therapeutic target also for ALS cases not linked to SOD1 mutation. Increased staining for S1R was detectable in morphologically spared cervical spinal cord motor neurons of wr mice both at early (6th week) and late (12th week) phases of clinical progression. S1R signal was also detectable in hypertrophic astrocytes and reactive microglia of wr mice. Chronic treatment with PRE-084 (three times a week, for 8weeks), starting at symptom onset, significantly increased the levels of BDNF in the gray matter, improved motor neuron survival and ameliorated paw abnormality and grip strength performance. In addition, the treatment significantly reduced the number of reactive astrocytes whereas, that of CD11b+ microglial cells was increased. A deeper evaluation of microglial markers revealed significant increased number of cells positive for the pan-macrophage marker CD68 and of CD206+ cells, involved in tissue restoration, in the white matter of PRE-084-treated mice. The mRNA levels of TNF-α and IL-1β were not affected by PRE-084 treatment. Thus, our results support pharmacological manipulation of S1R as a promising strategy to cure ALS and point to increased availability of growth factors and modulation of astrocytosis and of macrophage/microglia as part of the mechanisms involved in S1R-mediated neuroprotection.

Neuroprotective effects of toll-like receptor 4 antagonism in spinal cord cultures and in a mouse model of motor neuron degeneration

Sustained inflammatory reactions are common pathological events associated with neuron loss in neurodegenerative diseases. Reported evidence suggests that Toll-like receptor 4 (TLR4) is a key player of neuroinflammation in several neurodegenerative diseases. However, the mechanisms by which TLR4 mediates neurotoxic signals remain poorly understood. We investigated the role of TLR4 in in vitro and in vivo settings of motor neuron degeneration. Using primary cultures from mouse spinal cords, we characterized both the proinflammatory and neurotoxic effects of TLR4 activation with lipopolysaccharide (activation of microglial cells, release of proinflammatory cytokines and motor neuron death) and the protective effects of a cyanobacteria-derived TLR4 antagonist (VB3323). With the use of TLR4-deficient cells, a critical role of the microglial component with functionally active TLR4 emerged in this setting. The in vivo experiments were carried out in a mouse model of spontaneous motor neuron degeneration, the wobbler mouse, where we preliminarily confirmed a protective effect of TLR4 antagonism. Compared with vehicle- and riluzole-treated mice, those chronically treated with VB3323 showed a decrease in microglial activation and morphological alterations of spinal cord neurons and a better performance in the paw abnormality and grip-strength tests. Taken together, our data add new understanding of the role of TLR4 in mediating neurotoxicity in the spinal cord and suggest that TLR4 antagonists could be considered in future studies as candidate protective agents for motor neurons in degenerative diseases.

Human skeletal muscle stem cell antiinflammatory activity ameliorates clinical outcome in amyotrophic lateral sclerosis models

Mesenchymal stem cell (MSC) therapy is considered one of the most promising approaches for treating different neurodegenerative disorders, including amyotrophic lateral sclerosis (ALS). We previously characterized a subpopulation of human skeletal muscle-derived stem cells (SkmSCs) with MSC-like characteristics that differentiate into the neurogenic lineage in vitro. In the present study, we evaluated the SkmSC therapeutic effects in the most characterized model of spontaneous motor neuron degeneration, the Wobbler (Wr) mouse. Before evaluating the therapeutic efficacy in the Wr mouse, we followed the route of Skm-SCs at different times after intracerebroventricular injection. Two exogenous tracers, superparamagnetic iron oxide (SPIO) nanoparticles and Hoechst 33258, were used for the in vivo and ex vivo tracking of SkmSCs. We found that the loading of both Hoechst and SPIO was not toxic and efficiently labeled SkmSCs. The magnetic resonance imaging (MRI) system 7 Tesla allowed us to localize transplanted SkmSCs along the whole ventricular system up to 18 wks after injection. The ex vivo Hoechst 33258 visualization confirmed the in vivo results obtained by MRI analyses. Behavioral observations revealed a fast and sustained improvement of motor efficacy in SkmSC-treated Wr mice associated with a relevant protection of functional neuromuscular junctions. Moreover, we found that in SkmSC-treated Wr mice, a significant increase of important human antiinflammatory cytokines occurred. This evidence is in accordance with previous findings showing the bystander effect of stem cell transplantation in neurodegenerative disorders and further strengthens the hypothesis of the possible link between inflammation, cytotoxicity and ALS.

Longitudinal tracking of human fetal cells labeled with super paramagnetic iron oxide nanoparticles in the brain of mice with motor neuron disease

Stem Cell (SC) therapy is one of the most promising approaches for the treatment of Amyotrophic Lateral Sclerosis (ALS). Here we employed Super Paramagnetic Iron Oxide nanoparticles (SPIOn) and Hoechst 33258 to track human Amniotic Fluid Cells (hAFCs) after transplantation in the lateral ventricles of wobbler (a murine model of ALS) and healthy mice. By in vitro, in vivo and ex vivo approaches we found that: 1) the main physical parameters of SPIOn were maintained over time; 2) hAFCs efficiently internalized SPIOn into the cytoplasm while Hoechst 33258 labeled nuclei; 3) SPIOn internalization did not alter survival, cell cycle, proliferation, metabolism and phenotype of hAFCs; 4) after transplantation hAFCs rapidly spread to the whole ventricular system, but did not migrate into the brain parenchyma; 5) hAFCs survived for a long time in the ventricles of both wobbler and healthy mice; 6) the transplantation of double-labeled hAFCs did not influence mice survival.

Intracerebroventricular administration of human umbilical cord blood cells delays disease progression in two murine models of motor neuron degeneration

The lack of effective drug therapies for motor neuron diseases (MND), and in general for all the neurodegenerative disorders, has increased the interest toward the potential use of stem cells. Among the cell therapy approaches so far tested in MND animal models, systemic injection of human cord blood mononuclear cells (HuCB-MNCs) has proven to reproducibly increase, although modestly, the life span of SOD1G93A mice, a model of familial amyotrophic lateral sclerosis (ALS), even if only few transplanted cells were found in the damaged areas. In attempt to improve the potential efficacy of these cells in the central nervous system, we examined the effect and distribution of Hoechst 33258-labeled HuCB-MNCs after a single bilateral intracerberoventricular injection in two models of motor neuron degeneration, the transgenic SOD1G93A and wobbler mice. HuCB-MNCs significantly ameliorated symptoms progression in both mouse models and prolonged survival in SOD1G93A mice. They were localized in the lateral ventricles, even 4 months after administration. However, HuCB-MNCs were not found in the spinal cord ventral horns. This evidence strengthens the hypothesis that the beneficial role of transplanted cells is not due to cell replacement but is rather associated with the production and release of circulating protective factors that may act both at the central and/or peripheral levels. In particular, we show that HuCB-MNCs release a series of cytokines and chemokines with antiinflammatory properties that could be responsible of the functional improvement of mouse models of motor neuron degenerative disorders.

Amyotrophic lateral sclerosis pathogenesis: a journey through the secretory pathway

Amyotrophic lateral sclerosis (ALS) is the most common adult-onset motoneuron degenerative disease characterized by the selective loss of motoneurons in the spinal ventral horn, most brainstem nuclei, and the cerebral cortex. Although approximately 90% of ALS cases are sporadic (sALS), analyses of familial ALS (fALS)-causative genes have generated relevant insight into molecular events involved in the pathology. Here we overview an emerging concept indicating the occurrence of secretory pathway stress in the disease process. These alterations include a failure in the protein folding machinery at the endoplasmic reticulum (ER), engagement of the unfolded protein response (UPR), modifications of the Golgi apparatus network, impaired vesicular trafficking, inhibition of protein quality control mechanisms, oxidative damage to ER proteins, and sustained activation of degradative pathways such as autophagy. A common feature predicted for most of these alterations is abnormal protein homeostasis associated with the accumulation of misfolded proteins at the ER, possibly leading to chronic ER stress and neuronal dysfunction. Signs of ER stress are observed even during presymptomatic stages in fALS mouse models, and pharmacological strategies to alleviate protein misfolding slow disease progression. Because the secretory pathway stress occurs in both sALS and several forms of fALS, it may offer a unique common target for possible therapeutic strategies to treat this devastating disease.

Structural basis for the wobbler mouse neurodegenerative disorder caused by mutation in the Vps54 subunit of the GARP complex

The multisubunit Golgi-associated retrograde protein (GARP) complex is required for tethering and fusion of endosome-derived transport vesicles to the trans-Golgi network. Mutation of leucine-967 to glutamine in the Vps54 subunit of GARP is responsible for spinal muscular atrophy in the wobbler mouse, an animal model of amyotrophic lateral sclerosis. The crystal structure at 1.7 A resolution of the mouse Vps54 C-terminal fragment harboring leucine-967, in conjunction with comparative sequence analysis, reveals that Vps54 has a continuous alpha-helical bundle organization similar to that of other multisubunit tethering complexes. The structure shows that leucine-967 is buried within the alpha-helical bundle through predominantly hydrophobic interactions that are critical for domain stability and folding in vitro. Mutation of this residue to glutamine does not prevent integration of Vps54 into the GARP complex but greatly reduces the half-life and levels of the protein in vivo. Severely reduced levels of mutant Vps54 and, consequently, of the whole GARP complex underlie the phenotype of the wobbler mouse.

Experimental models for the study of neurodegeneration in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease of unknown cause, characterized by the selective and progressive death of both upper and lower motoneurons, leading to a progressive paralysis. Experimental animal models of the disease may provide knowledge of the pathophysiological mechanisms and allow the design and testing of therapeutic strategies, provided that they mimic as close as possible the symptoms and temporal progression of the human disease. The principal hypotheses proposed to explain the mechanisms of motoneuron degeneration have been studied mostly in models in vitro, such as primary cultures of fetal motoneurons, organotypic cultures of spinal cord sections from postnatal rodents and the motoneuron-like hybridoma cell line NSC-34. However, these models are flawed in the sense that they do not allow a direct correlation between motoneuron death and its physical consequences like paralysis. In vivo, the most widely used model is the transgenic mouse that bears a human mutant superoxide dismutase 1, the only known cause of ALS. The major disadvantage of this model is that it represents about 2%-3% of human ALS. In addition, there is a growing concern on the accuracy of these transgenic models and the extrapolations of the findings made in these animals to the clinics. Models of spontaneous motoneuron disease, like the wobbler and pmn mice, have been used aiming to understand the basic cellular mechanisms of motoneuron diseases, but these abnormalities are probably different from those occurring in ALS. Therefore, the design and testing of in vivo models of sporadic ALS, which accounts for >90% of the disease, is necessary. The main models of this type are based on the excitotoxic death of spinal motoneurons and might be useful even when there is no definitive demonstration that excitotoxicity is a cause of human ALS. Despite their difficulties, these models offer the best possibility to establish valid correlations between cellular alterations and motor behavior, although improvements are still necessary in order to produce a reliable and integrative model that accurately reproduces the cellular mechanisms of motoneuron degeneration in ALS.