Comparative study of behavioural tests in the SOD1G93A mouse model of amyotrophic lateral sclerosis

In preclinical trials, a sensitive functional test is required to detect changes in the motor behaviour of the SOD1G93A mouse model of amyotrophic lateral sclerosis (ALS). We evaluated changes in body weight and motor impairment in behavioural tests, such as the rotarod, the hanging-wire test and the treadmill, of transgenic and wild type mice. We found differences in detection of the onset of symptoms and progression of the disease between the different tests assessed. Moreover, the data showed significant gender differences in the motor behaviour of this mouse model. The rotarod and the hanging-wire test were more sensitive to detect early motor impairment. Moreover, the results suggested that the rotarod and hanging-wire became the most accurate tests rather than treadmill to characterise the ALS disease phenotype.     

Arylsulfanyl pyrazolones block mutant SOD1-G93A aggregation. Potential application for the treatment of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is an orphan neurodegenerative disease currently without a cure. Mutations in copper/zinc superoxide dismutase 1 (SOD1) have been implicated in the pathophysiology of this disease. Using a high-throughput screening assay expressing mutant G93A SOD1, two bioactive chemical hit compounds (1 and 2), identified as arylsulfanyl pyrazolones, were identified. The structural optimization of this scaffold led to the generation of a more potent analogue (19) with an EC₅₀ of 170 nM. To determine the suitability of this class of compounds for further optimization, 1 was subjected to a battery of pharmacokinetic assays; most of the properties of 1 were good for a screening hit, except it had a relatively rapid clearance and short microsomal half-life stability. Compound 2 was found to be blood-brain barrier penetrating with a brain/plasma ratio = 0.19. The optimization of this class of compounds could produce novel therapeutic candidates for ALS patients.     

S-nitrosylated GAPDH mediates neuronal apoptosis induced by amyotrophic lateral sclerosis-associated mutant SOD1G93A

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease with the selective loss of motor neurons in the brain, brain stem, and spinal cord. A number of the mutants of the human gene for superoxide dismutase 1 (SOD1) have been shown to cause familial ALS as a result of gain-of-function toxicity by an unknown mechanism. In this study, we show that glyceraldehyde-3-phosphate dehydrogenase (GAPDH) functions as a critical mediator of the apoptotic cell death signaling cascade induced by the ALS-associated G93A mutant of human SOD1 [SOD1(G93A)]. We observed that SOD1(G93A) induces S-nitrosylation of GAPDH and the subsequent binding of GAPDH and Siah1 in NSC34 motor neuron-like cells. Furthermore, SOD1(G93A) promoted nuclear translocation of S-nitrosylated GAPDH in the cells. In addition, SOD1(G93A)-induced apoptotic cell death was inhibited by deprenyl, a chemical inhibitor of GAPDH S-nitrosylation, in NSC34 cells. Taken together, our findings suggest that S-nitrosylation of GAPDH plays a critical role in SOD1(G93A)-induced neuronal apoptosis.     

Presymptomatic and symptomatic ALS SOD1(G93A) mice differ in adenosine A1 and A2A receptor-mediated tonic modulation of neuromuscular transmission

Amyotrophic lateral sclerosis (ALS) is a disease leading to neuromuscular transmission impairment. A_2A adenosine receptor (A2AR) function changes with disease stage, but the role of the A₁ receptors (A1Rs) is unknown and may have a functional cross-talk with A2AR. The role of A1R in the SOD1(G93A) mouse model of ALS in presymptomatic (4–6 weeks old) and symptomatic (12–14 weeks old) phases was investigated by recording endplate potentials (EPPs), miniature endplate potentials (MEPPs), and quantal content (q.c.) of EPPs, from Mg²⁺ paralyzed hemidiaphragm preparations. In presymptomatic mice, the A1R agonist, N⁶-cyclopentyladenosine (CPA) (50 nM), decreased mean EPP amplitude, MEPP frequency, and q.c. of EPPs, an effect quantitatively similar to that in age-matched wild-type (WT) mice. However, coactivation of A2AR with CGS 21680 (5 nM) prevented the effects of CPA in WT mice but not in presymptomatic SOD1(G93A) mice, suggestive of A1R/A2AR cross-talk disruption in this phase of ALS. DPCPX (50 nM) impaired CGS 21680 facilitatory action on neuromuscular transmission in WT but not in presymptomatic mice. In symptomatic animals, CPA only inhibited transmission if added in the presence of adenosine deaminase (ADA, 1 U/mL). ADA and DPCPX enhanced more transmission in symptomatic mice than in age-matched WT mice, suggestive of increase in extracellular adenosine during the symptomatic phase of ALS. The data documents that at the neuromuscular junction of presymptomatic SOD1(G93A) mice, there is a loss of A1R-A2AR functional cross-talk, while in symptomatic mice there is increased A1R tonic activation, and that with disease progression, changes in A1R-mediated adenosine modulation may act as aggravating factors during the symptomatic phase of ALS.     

Proteomic analysis of spinal cord of presymptomatic amyotrophic lateral sclerosis G93A SOD1 mouse

Amyotrophic lateral sclerosis (ALS) is a fatal motor neuron disease, whose primary mechanisms or causes are still not defined and for which no effective treatment is available. We have recently reported that before disease onset the level of tyrosine nitrated proteins is increased in the G93A SOD1 transgenic mouse model of ALS. In the present investigation, we carried out a proteomic analysis of spinal cord extracts from G93A SOD1 mice at the presymptomatic stage of the disease to further unravel primary events in the pathogenesis and tentatively screen for potential pharmacological targets. Using a robust two-dimensional gel electrophoresis-based proteomic approach, we detected a number of proteins differentially represented in presymptomatic mice in comparison with controls. Alterations of these proteins correlate with mitochondrial dysfunction, aggregation, and stress response. Moreover, we found a variation in the isoform pattern of cyclophilin A, a molecular chaperone that protects cells from the oxidative stress.     

Immunohistochemical localization of insulin-like growth factor binding protein 2 in the central nervous system of SOD1<Superscript>G93A</Superscript> transgenic mice

In the present study, we performed immunohistochemical studies to investigate the changes of insulin-like growth factor binding protein 2 (IGFBP2) in the central nervous system of SOD1^G93A mutant transgenic mice as an in vivo model of amyotrophic lateral sclerosis (ALS). Decreased immunoreactivity for IGFBP2 was observed in the cerebral cortex, hippocampus and brainstem of SOD1^G93A transgenic mice. In the cerebral cortex, the number of IGFBP2-positive cells was decreased in the somatomotor area, somatosensory area, auditory area, visual area, entorhinal area, piriform area and prefrontal area. In the hippocampal formation, IGFBP2 immunoreactivity was significantly decreased in the CA1-3 areas and the dentate gyrus. In the brainstem, few IGFBP2-immunoreactive cells were observed in the medullary and pontine reticular formation, vestibular nucleus, trigeminal motor nucleus, facial nucleus, hypoglossal nucleus and raphe nucleus. In the spinal cord, IGFBP2 immunoreactivity was not significantly decreased in SOD1^G93A transgenic mice. This study showing decreased IGFBP2 in different brain regions of SOD1^G93A transgenic mice may provide clues for understanding differential susceptibility of neural structures in ALS. S. E. Sim and Y. H. Chung have contributed equally to this work.     

Exploring the cause of aggregation and reduced Zn binding affinity by G85R mutation in SOD1 rendering amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS), a lethal neurodegenerative disorder is characterized by the degeneration of upper and lower motor neuron. ALS occurs due to various notably prominent missense mutations, in gene encoding Cu‐Zn superoxide dismutase (SOD1) thereby leading to aggregation, dysfunction and reduced Zn binding affinity. In this study, one such mutation, G85R was explored in comparison with wild type SOD1, using discrete molecular dynamics (DMD). Accordingly, the conformational changes were significantly observed in mutant SOD1, through various geometrical parameters, which substantiated the difference in conformational deviation, flexibility and compactness, thus stipulating a root cause for aggregation. Followed by, analysis of essential dynamics further authenticated the cause behind the protein dysfunction. In particular, the high content of beta sheet with structural deviations, down to dysfunction was established in mutant as compared to wild type, while passing through secondary structure analysis. Subsequently, the deviation of distance in Zn binding residues was distinctly portrayed in mutant as compared to wild type, thus confirming the cause of reduced Zn binding affinity. In addition, the steered molecular dynamics analysis also authenticated the above results indicating the reduced Zn binding affinity in the mutant as compared to that of the wild type. Hence, this work revealed the theoretical mechanism to unravel the mutational effects of cofactor dependent protein. Proteins 2017; 85:1276–1286. © 2017 Wiley Periodicals, Inc.     

Human adipose-derived stem cells enhance the glutamate uptake function of GLT1 in SOD1-bearing astrocytes

Impaired glutamate uptake function of astrocytes associated with accumulation of extracellular glutamate is a well-documented feature of amyotrophic lateral sclerosis (ALS). Enhancing the uptake function of astrocytic glutamate transport 1 (GLT1) may be a potential treatment for this disease. Human adipose-derived stem cells (hADSCs) are capable of secreting a large number of cytokines which exhibit diverse pharmacological effects. Therefore, we investigate the influence of the soluble factors released by hADSCs on the GLT1 in primary astrocytes cultured from SOD1^G93A mice, a widely studied mutant human SOD1 transgenic model of ALS. Our data indicate that soluble factors from hADSCs significantly upregulate the expression of GLT1 in SOD1^G93A-bearing astrocytes, which result in enhanced glutamate uptake function. The upregulation of GLT1 is accompanied by the inhibition of caspase-3 activation in mutant astrocytes. In addition, we find that hADSCs cocultured with SOD1^G93A-bearing astrocytes produce more VEGF, HGF and IGF-1, which are reported to have neuroprotective effects. Our results suggest that hADSCs may be a potential candidate in cellular therapy for ALS.     

Surface Trafficking of APP and BACE in Live Cells

Amyloid‐β (Aβ)‐peptide, the major constituent of the plaques that develop during Alzheimer's disease, is generated via the cleavage of Aβ precursor protein (APP) by β‐site APP‐cleaving enzyme (BACE). Using live‐cell imaging of APP and BACE labeled with pH‐sensitive proteins, we could detect the release events of APP and BACE and their distinct kinetics. We provide kinetic evidence for the cleavage of APP by α‐secretase on the cellular surface after exocytosis. Furthermore, simultaneous dual‐color evanescent field illumination revealed that the two proteins are trafficked to the surface in separate compartments. Perturbing the membrane lipid composition resulted in a reduced frequency of exocytosis and affected BACE more strongly than APP. We propose that surface fusion frequency is a key factor regulating the aggregation of APP and BACE in the same membrane compartment and that this process can be modulated via pharmacological intervention.      

Abnormal medial prefrontal cortex connectivity and defective fear extinction in the presymptomatic G93A SOD1 mouse model of ALS

Amyotrophic lateral sclerosis (ALS) is a fatal progressive neuropathy associated with the degeneration of spinal and brainstem motor neurons. Although ALS is essentially considered as a lower motor neuron disease, prefrontal cortex atrophy underlying executive function deficits have been extensively reported in ALS patients. Here, we examine whether prefrontal cortex neuronal abnormalities and related cognitive impairments are present in presymptomatic G93A Cu/Zn superoxide dismutase mice, a mouse model for familial ALS. Structural characteristics of prelimbic/infralimbic (PL/IL) medial prefrontal cortex (mPFC) neurons were studied in 3-month-old G93A and wild-type mice with the Golgi–Cox method, while mPFC-related cognitive operations were assessed using the conditioned fear extinction paradigm. Sholl analysis performed on the dendritic material showed a reduction in dendrite length and branch nodes on basal dendrites of PL/IL neurons in G93A mice. Spine density was also decreased on basal dendrite segments of branch order five. Consistent with the altered morphology of PL/IL cortical regions, G93A mice showed impaired extinction of conditioned fear. Our findings indicate that abnormal prefrontal cortex connectivity and function are appreciable before the onset of motor disturbances in this model.     

Elevated cortical extracellular fluid glutamate in transgenic mice expressing human mutant (G93A) Cu/Zn superoxide dismutase

Transgenic mice expressing a mutated (G93A) human Cu/Zn superoxide dismutase (SOD1) develop motor neuron pathology and clinical symptoms similar to those seen in patients with amyotrophic lateral sclerosis. Loss of motor neurons is most prominent in lumbar, followed by cervical cord and then brainstem. No significant cell death has been reported in motor cortex. The integrity of the cortical glutamate reuptake systems was evaluated using intracerebral microdialysis and western immunoblot assays for the glutamate transporters GLT-1, GLAST, and EAAC1. The basal extracellular fluid levels of aspartate, glutamate, glutamine, 3,4-dihydroxyphenylacetic acid, and 5-hydroxyindole-3-acetic acid were evaluated by HPLC. The extraction fraction of L-3H]glutamate, corrected with [14C]mannitol, was also evaluated. GLT-1, EAAC1, and GLAST protein levels were determined by semiquantitative chemiluminescence immunoblot of proteins from membrane-enriched fractions. The relative optical density of film was translated into relative protein level by comparison with a standard control mouse. The SOD1 mutant mice demonstrated a significant (p < 0.05) increase in basal levels of extracellular aspartate and glutamate. In addition, when the glutamate extraction fraction was challenged with exogenous unlabeled glutamate (500 microM) by reversed microdialysis, the glutamate extraction fraction in the mutant SOD1 mice was decreased significantly from control levels. The SOD1 mutant mice demonstrated no difference in the cortical protein levels of the glutamate transporter subtypes. This study demonstrates that in areas of no visible pathology and no loss of glutamate transporter proteins, SOD1 mutant mice have elevated extracellular fluid aspartate and glutamate levels and a decreased capacity to clear glutamate from the extracellular space.     

Motor neuronal protection by l-arginine prolongs survival of mutant SOD1 (G93A) ALS mice

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder characterized by progressive paralysis due to motor neuron degeneration. Despite the fact that many different therapeutic strategies have been applied to prevent disease progression, no cure or effective therapy is currently available for ALS. We found that l-arginine protects cultured motor neurons from excitotoxic injury. We also found that l-arginine supplementation both prior to and after the onset of motor neuron degeneration in mtSOD1 (G93A) transgenic ALS mice significantly slowed the progression of neuropathology in lumbar spinal cord, delayed onset of motor dysfunction, and prolonged life span. Moreover, l-arginine treatment was associated with preservation of arginase I activity and neuroprotective polyamines in spinal cord motor neurons. Our findings show that l-arginine has potent in vitro and in vivo neuroprotective properties and may be a candidate for therapeutic trials in ALS.     

Abnormal exocytotic release of glutamate in a mouse model of amyotrophic lateral sclerosis

Glutamate-mediated excitotoxicity plays a major role in the degeneration of motor neurons in amyotrophic lateral sclerosis and reduced astrocytary glutamate transport, which in turn increases the synaptic availability of the amino acid neurotransmitter, was suggested as a cause. Alternatively, here we report our studies on the exocytotic release of glutamate as a possible source of excessive glutamate transmission. The basal glutamate efflux from spinal cord nerve terminals of mice-expressing human soluble superoxide dismutase (SOD1) with the G93A mutation [SOD1/G93A(+)], a transgenic model of amyotrophic lateral sclerosis, was elevated when compared with transgenic mice expressing the wild-type human SOD1 or to non-transgenic controls. Exposure to 15 mM KCl or 0.3 μM ionomycin provoked Ca(2+)-dependent glutamate release that was dramatically increased in late symptomatic and in pre-symptomatic SOD1/G93A(+) mice. Increased Ca(2+) levels were detected in SOD1/G93A(+) mouse spinal cord nerve terminals, accompanied by increased activation of Ca(2+)/calmodulin-dependent kinase II and increased phosphorylation of synapsin I. In line with these findings, release experiments suggested that the glutamate release augmentation involves the readily releasable pool of vesicles and a greater capability of these vesicles to fuse upon stimulation in SOD1/G93A(+) mice.     

Mutant SOD1 linked to familial amyotrophic lateral sclerosis,but not wild-type SOD1, induces ER stress in COS7 cells and transgenic mice

Mutations in a Cu, Zn-superoxide dismutase (SOD1) cause motor neuron death in human familial amyotrophic lateral sclerosis (FALS) and its mouse model, suggesting that mutant SOD1 has a toxic effect on motor neurons. However, the question of how the toxic function is gained has not been answered. Here, we report that the mutant SOD1s linked to FALS, but not wild-type SOD1, aggregated in association with the endoplasmic reticulum (ER) and induced ER stress in the cDNA-transfected COS7 cells. These cells showed an aberrant intracellular localization of mitochondria and microtubules, which might lead to a functional disturbance of the cells. Motor neurons of the spinal cord in transgenic mice with a FALS-linked mutant SOD1 also showed a marked increase of GRP78/BiP, an ER-resident chaperone, just before the onset of motor symptoms. These data suggest that ER stress is involved in the pathogenesis of FALS with an SOD1 mutation.     

Decreased GLT-1 and increased SOD1 and HO-1 expression in astrocytes contribute to lumbar spinal cord vulnerability of SOD1-G93A transgenic mice

The SOD1-G93A transgenic mouse is a widely used ALS model, but the death of lower motor neurons is the hallmark. Here, we show that the SOD1-G93A transgene and HO-1 are preferentially over-expressed in the lumbar spinal cord, particularly in the activated astrocytes of the transgenic mice. We also show down-regulation of GLT-1 in spite of the proliferating astrocytes. However, GLT-1, SOD1-G93A transgene and HO-1 expression were not obviously changed in the motor cortex. Our data link spinal cord vulnerability to relatively decreased expression of GLT-1, and high expression of the transgene and HO-1 in astrocytes in SOD1-G93A transgenic mice.     

Mutant SOD1(G93A) microglia are more neurotoxic relative to wild-type microglia

Recent studies suggest that microglia over-expressing mutant human superoxide dismutase (mSOD1(G93A)) may contribute to motoneuron death in a transgenic mouse model of familial amyotrophic lateral sclerosis. To further assess the relative neurotoxicity of wild-type microglia, mSOD1(G93A) microglia, and microglia over-expressing wild-type human SOD1, we used primary cultures of microglia and motoneurons in the presence and absence of lipopolysaccharide stimulation. Following activation with lipopolysaccharide, mSOD1(G93A) microglia released more nitric oxide, more superoxide, and less insulin-like growth factor-1 than wild-type microglia. In microglia/motoneuron co-cultures, mSOD1(G93A) microglia induced more motoneuron death and decreased neurite numbers and length compared with wild-type microglia. Mutant SOD1(G93A) microglia also induced more motoneuron injury than microglia over-expressing wild-type human SOD1 in microglia/motoneuron co-cultures. Motoneuron survival was inversely correlated with nitrate + nitrite concentrations in mSOD1(G93A) co-cultures, suggesting the important role of nitric oxide in microglia-induced motoneuron injury. Thus, relative to wild-type microglia, mSOD1(G93A) microglia were more neurotoxic and induced more motoneuron injury than similarly treated wild-type microglia.     

Endocannabinoids accumulate in spinal cord of SOD1 G93A transgenic mice

Approximately 2% of amyotrophic lateral sclerosis (ALS) cases are caused by mutations in the super oxide dismutase 1 (SOD1) gene and transgenic mice for these mutations recapitulate many features of this devastating neurodegenerative disease. Here we show that the amount of anandamide (AEA) and 2-arachidonoylglycerol (2-AG), two endocannabinoids that have neuroprotective properties, increase in spinal cord of SOD1(G93A) transgenic mice. This increase occurs in the lumbar section of spinal cords, the first section to undergo neurodegeneration, and is significant before overt motor impairment. Our results show that chronic neurodegeneration induced by a genetic mutation increases endocannabinoid production possibly as part of an endogenous defense mechanism.     

Characterizing the multiple roles of FGF-2 in SOD1G93A ALS mice in vivo and in vitro

We have previously shown that knockout of fibroblast growth factor-2 (FGF-2) and potential compensatory effects of other growth factors result in amelioration of disease symptoms in a transgenic mouse model of amyotrophic lateral sclerosis (ALS). ALS is a rapidly progressive neurological disorder leading to degeneration of cortical, brain stem, and spinal motor neurons followed by subsequent denervation and muscle wasting. Mutations in the superoxide dismutase 1 (SOD1) gene are responsible for approximately 20% of familial ALS cases and SOD1 mutant mice still are among the models best mimicking clinical and neuropathological characteristics of ALS. The aim of the present study was a thorough characterization of FGF-2 and other growth factors and signaling effectors in vivo in the SOD1^G93A mouse model. We observed tissue-specific opposing gene regulation of FGF-2 and overall dysregulation of other growth factors, which in the gastrocnemius muscle was associated with reduced downstream extracellular-signal-regulated kinases (ERK) and protein kinase B (AKT) activation. To further investigate whether the effects of FGF-2 on motor neuron death are mediated by glial cells, astrocytes lacking FGF-2 were cocultured together with mutant SOD1 ^G93A motor neurons. FGF-2 had an impact on motor neuron maturation indicating that astrocytic FGF-2 affects motor neurons at a developmental stage. Moreover, neuronal gene expression patterns showed FGF-2- and SOD1 ^G93A-dependent changes in ciliary neurotrophic factor, glial-cell-line-derived neurotrophic factor, and ERK2, implying a potential involvement in ALS pathogenesis before the onset of clinical symptoms.     

A hyperthermophilic protein G variant engineered via directed evolution prevents the formation of toxic SOD1 oligomers

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder characterized by selective death of motor neurons in the brainstem, motor cortex, and spinal cord, leading to muscle atrophy and eventually to death. It is currently held that various oligomerization-inducing mutations in superoxide dismutase 1 (SOD1), an amyloid-forming protein, may be implicated in the familial form of this fast-progressing highly lethal neurodegenerative disease. A possible therapeutic approach could therefore lie in developing inhibitors to SOD1 mutants. By screening a focused mutagenesis library, mutated randomly in specific “stability patch” positions of the B1 domain of protein G (HTB1), we previously identified low affinity inhibitors of aggregation of SOD1_G93A and SOD1_G85R mutants. Herein, with the aim to generate a more potent inhibitor with higher affinity to SOD1 mutants, we employed an unbiased, random mutagenesis approach covering the entire sequence space of HTB1 to optimize as yet undefined positions for improved interactions with SOD1. Using affinity maturation screens in yeast, we identified a variant, which we designated HTB1_M3, that bound strongly to SOD1 misfolded mutants but not to wild-type SOD1. In-vitro aggregation assays indicated that in the presence of HTB1_M3 misfolded SOD1 assembled into oligomeric species that were not toxic to NSC-34 neuronal cells. In addition, when NSC-34 cells were exposed to misfolded SOD1 mutants, either soluble or preaggregated, in the presence of HTB1_M3, this inhibitor prevented the prion-like propagation of SOD1 from one neuronal cell to another by blocking the penetration of SOD1 into the neuronal cells.