Canine degenerative myelopathy: biochemical characterization of superoxide dismutase 1 in the first naturally occurring non-human amyotrophic lateral sclerosis model

The usage and advantages of several common amyotrophic lateral sclerosis animal models

Amyotrophic lateral sclerosis is a fatal, multigenic, multifactorial neurodegenerative disease characterized by upper and lower motor neuron loss. Animal models are essential for investigating pathogenesis and reflecting clinical manifestations, particularly in developing reasonable prevention and therapeutic methods for human diseases. Over the decades, researchers have established a host of different animal models in order to dissect amyotrophic lateral sclerosis (ALS), such as yeast, worms, flies, zebrafish, mice, rats, pigs, dogs, and more recently, non-human primates. Although these models show different peculiarities, they are all useful and complementary to dissect the pathological mechanisms of motor neuron degeneration in ALS, contributing to the development of new promising therapeutics. In this review, we describe several common animal models in ALS, classified by the naturally occurring and experimentally induced, pointing out their features in modeling, the onset and progression of the pathology, and their specific pathological hallmarks. Moreover, we highlight the pros and cons aimed at helping the researcher select the most appropriate among those common experimental animal models when designing a preclinical ALS study.

Pathological insights from amyotrophic lateral sclerosis animal models: comparisons, limitations, and challenges

In order to dissect amyotrophic lateral sclerosis (ALS), a multigenic, multifactorial, and progressive neurodegenerative disease with heterogeneous clinical presentations, researchers have generated numerous animal models to mimic the genetic defects. Concurrent and comparative analysis of these various models allows identification of the causes and mechanisms of ALS in order to finally obtain effective therapeutics. However, most genetically modified rodent models lack overt pathological features, imposing challenges and limitations in utilizing them to rigorously test the potential mechanisms. Recent studies using large animals, including pigs and non-human primates, have uncovered important events that resemble neurodegeneration in patients' brains but could not be produced in small animals. Here we describe common features as well as discrepancies among these models, highlighting new insights from these models. Furthermore, we will discuss how to make rodent models more capable of recapitulating important pathological features based on the important pathogenic insights from large animal models.

Prevalence of SOD1 allele associated with degenerative myelopathy in canine population in Greece

Canine degenerative myelopathy (CDM) is a late-onset fatal disorder associated with a point mutation of the superoxide dismutase 1 (SOD1) gene (c.118G > A). The purpose of this study was to determine the genotype and allele frequencies of this mutation in 108 dogs, mainly in Belgian Malinois and German Shepherd dogs with (CDM-affected group) and without CDM clinical symptoms (control group) in Greece. Genotyping of the c.118G > A mutation was possible by Sanger sequencing and PCR-RFLP. The observed genotype frequencies for the control group were 89.4% for the homozygous (G/G), 9.6% for the heterozygous (A/G), and 0.96% for the homozygous mutant (A/A) allele. The mutant allele was not common in the Belgian Malinois dogs (allele frequency = 0.029), but quite common in the German Shepherd dogs (allele frequency = 0.138). In the CDM affected group, all 4 dogs were homozygous for the mutant allele. These frequencies were close to those expected, indicating no significant departure from Hardy-Weinberg equilibrium. A strong but not statistically significant association between the mutant allele and CDM was observed. A previously identified deletion upstream of the mutation of interest was found at a high frequency (0.361) in the population.

Intensive neurorehabilitation and allogeneic stem cells transplantation in canine degenerative myelopathy

Introduction

Degenerative myelopathy (DM) is a neurodegenerative spinal cord disease with upper motor neurons, with progressive and chronic clinical signs, similar to amyotrophic lateral sclerosis (ALS). DM has a complex etiology mainly associated with SOD1 gene mutation and its toxic role, with no specific treatment. Daily intensive rehabilitation showed survival time near 8 months but most animals are euthanized 6-12 months after clinical signs onset.

Methods

This prospective controlled blinded cohort clinical study aims to evaluate the neural regeneration response ability of DM dogs subjected to an intensive neurorehabilitation protocol with mesenchymal stem cells (MSCs) transplantation. In total, 13 non-ambulatory (OFS 6 or 8) dogs with homozygous genotype DM/DM and diagnosed by exclusion were included. All were allocated to the intensive neurorehabilitation with MSCs protocol (INSCP) group (n = 8) or to the ambulatory rehabilitation protocol (ARP) group (n = 5), which differ in regard to training intensity, modalities frequency, and MSCs transplantation. The INSCP group was hospitalized for 1 month (T0 to T1), followed by MSCs transplantation (T1) and a second month (T2), whereas the ARP group was under ambulatory treatment for the same 2 months.

Results

Survival mean time of total population was 375 days, with 438 days for the INSCP group and 274 for the ARP group, with a marked difference on the Kaplan-Meier survival analysis. When comparing the literature's results, there was also a clear difference in the one-sample t-test (p = 0.013) with an increase in time of approximately 70%. OFS classifications between groups at each time point were significantly different (p = 0.008) by the one-way ANOVA and the independent sample t-test.

Discussion

This INSCP showed to be safe, feasible, and a possibility for a long progression of DM dogs with quality of life and functional improvement. This study should be continued.

Intrinsic structural vulnerability in the hydrophobic core induces species-specific aggregation of canine SOD1 with degenerative myelopathy-linked E40K mutation

Canine degenerative myelopathy (DM), a fatal neurodegenerative disease in dogs, shares clinical and genetic features with amyotrophic lateral sclerosis (ALS), a human motor neuron disease. Mutations in the SOD1 gene encoding Cu/Zn superoxide dismutase (SOD1) cause canine DM and a subset of inherited human ALS. The most frequent DM causative mutation is homozygous E40K mutation which induces the aggregation of canine SOD1 but not of human SOD1. However, the mechanism through which canine E40K mutation induces species-specific aggregation of SOD1 remains unknown. By screening human/canine chimeric SOD1s, we identified that the humanized mutation of the 117th residue (M117L), encoded by exon 4, significantly reduced aggregation propensity of canine SOD1^E40K. Conversely, introducing a mutation of leucine 117 to methionine, a residue homologous to canine, promoted E40K-dependent aggregation in human SOD1. M117L mutation improved protein stability and reduced cytotoxicity of canine SOD1^E40K. Furthermore, crystal structural analysis of canine SOD1 proteins revealed that M117L increased the packing within the hydrophobic core of the β-barrel structure, contributing to the increased protein stability. Our findings indicate that the structural vulnerability derived intrinsically from Met 117 in the hydrophobic core of the β-barrel structure induces E40K-dependent species-specific aggregation in canine SOD1.

The inhibitory effects of MIF on accumulation of canine degenerative myelopathy-associated mutant SOD1 aggregation

Canine degenerative myelopathy (DM) is a progressive neurodegenerative disorder, which is commonly associated with c.118G > A (p. E40K) missense mutation in the superoxide dismutase 1 (SOD1) gene. Mutant SOD1 protein (SOD1E40K) is likely to be misfolded, acquire insolubility, aggregate in the cytoplasm of neural cells, and lead to degeneration of the nervous tissues. Along with a chaperone activity, macrophage migration inhibitory factor (MIF) is a multifunctional protein that has been shown to directly inhibit human mutant SOD1 misfolding and enhance survival of mutant SOD1-expressing motor neurons. The purpose of this study was to determine whether MIF also inhibits DM-related SOD1E40K misfolding and accumulation of SOD1 aggregates. Human embryonic kidney 293A cells were transfected SOD1cWT or SOD1E40K with or without MIF. The percentages of cells containing transfected SOD1 aggregates were measured by immunocytochemistry, and the amount of SOD1E40K in the insoluble fraction was evaluated by immunoblotting. The percentage of cells with SOD1E40K aggregates and the amount of insoluble SOD1E40K protein decreased in the presence of MIF. Because the chaperone activity of MIF assists in SOD1E40K folding and enhances the refolding and degradation of misfolded SOD1E40K, the results of this study suggests that MIF regulates the accumulation of SOD1 aggregates by its chaperone activity. We propose that enhancing intracellular MIF chaperone activity could be an effective therapeutic strategy for DM.

Nearly 30 Years of Animal Models to Study Amyotrophic Lateral Sclerosis: A Historical Overview and Future Perspectives

Amyotrophic lateral sclerosis (ALS) is a fatal, multigenic, multifactorial, and non-cell autonomous neurodegenerative disease characterized by upper and lower motor neuron loss. Several genetic mutations lead to ALS development and many emerging gene mutations have been discovered in recent years. Over the decades since 1990, several animal models have been generated to study ALS pathology including both vertebrates and invertebrates such as yeast, worms, flies, zebrafish, mice, rats, guinea pigs, dogs, and non-human primates. Although these models show different peculiarities, they are all useful and complementary to dissect the pathological mechanisms at the basis of motor neuron degeneration and ALS progression, thus contributing to the development of new promising therapeutics. In this review, we describe the up to date and available ALS genetic animal models, classified by the different genetic mutations and divided per species, pointing out their features in modeling, the onset and progression of the pathology, as well as their specific pathological hallmarks. Moreover, we highlight similarities, differences, advantages, and limitations, aimed at helping the researcher to select the most appropriate experimental animal model, when designing a preclinical ALS study.

The Long-Term Clinical Course of Canine Degenerative Myelopathy and Therapeutic Potential of Curcumin

Canine degenerative myelopathy (DM), recognized as a spontaneous model of amyotrophic lateral sclerosis, is known as a late-onset progressive degenerative disease of the spinal cord. Because of the progressive nature of DM, many dogs are elected to be euthanized, resulting in limited information on the end-stage clinical presentation. We investigated the long-term clinical course from diagnosis to natural death to further deepen our understanding of the entire clinical picture of this disease. Because curcumin was administered in some cases, the therapeutic effect of curcumin on DM was also examined. Forty dogs included in this study were client-owned Pembroke Welsh Corgis with a definitive diagnosis of DM by necropsy and histopathology. Dogs were excluded from this study if they died from another disease or were elected to be euthanized. Information on the long-term clinical symptoms of DM was investigated based on a questionnaire, which was collected from the dog owners. Urinary incontinence and respiratory disorder were observed in most dogs, as was respiratory impairment-correlated death. In contrast, signs consistent with brainstem dysfunction were noticed at the terminal stage in a small portion of dogs. Although further studies with more cases are needed, the results of this study suggest that administration of curcumin is effective in slowing the progression of DM.

In vitro evidence of propagation of superoxide dismutase-1 protein aggregation in canine degenerative myelopathy

Canine degenerative myelopathy (DM) is a progressive and fatal neurodegenerative disorder that has been linked to mutations in the superoxide dismutase 1 (SOD1) gene. The accumulation of misfolded protein aggregates in spinal neurons and astrocytes is implicated as an important pathological process in DM; however, the mechanism of protein aggregate formation is largely unknown. In human neurodegenerative diseases, such as amyotrophic lateral sclerosis (ALS), cell-to-cell propagation of disease-relevant proteins has been demonstrated. Therefore, in this study, propagation of aggregation-forming property of mutant SOD1 protein in DM in vitro was investigated. This study demonstrated that aggregates composed of canine wild type SOD1 protein were increased by co-transfection with canine mutant SOD1 (E40K SOD1), indicating intracellular propagation of SOD1 aggregates. Further, aggregated recombinant SOD1 proteins were released from the cells, taken up by other cells, and induced further aggregate formation of normally folded SOD1 proteins. These results suggest intercellular propagation of SOD1 aggregates. The hypothesis of cell-to-cell propagation of SOD1 aggregates proposed in this study may underly the progressive nature of DM pathology.

Where and Why Modeling Amyotrophic Lateral Sclerosis

Over the years, researchers have leveraged a host of different in vivo models in order to dissect amyotrophic lateral sclerosis (ALS), a neurodegenerative/neuroinflammatory disease that is heterogeneous in its clinical presentation and is multigenic, multifactorial and non-cell autonomous. These models include both vertebrates and invertebrates such as yeast, worms, flies, zebrafish, mice, rats, guinea pigs, dogs and, more recently, non-human primates. Despite their obvious differences and peculiarities, only the concurrent and comparative analysis of these various systems will allow the untangling of the causes and mechanisms of ALS for finally obtaining new efficacious therapeutics. However, harnessing these powerful organisms poses numerous challenges. In this context, we present here an updated and comprehensive review of how eukaryotic unicellular and multicellular organisms that reproduce a few of the main clinical features of the disease have helped in ALS research to dissect the pathological pathways of the disease insurgence and progression. We describe common features as well as discrepancies among these models, highlighting new insights and emerging roles for experimental organisms in ALS.

Up-regulated spinal microRNAs induce aggregation of superoxide dismutase 1 protein in canine degenerative myelopathy

Canine degenerative myelopathy (DM) is a fatal progressive neurodegenerative disease. Mutations in the superoxide dismutase 1 (SOD1) gene have been shown to be the major risk factor for DM, and it is hypothesized that neural degeneration is caused by a "gain of toxic function" of mutant SOD1. In this study, the spinal cord microRNA (miRNA) profiles of DM-affected dogs were investigated to elucidate the pathomechanisms of DM. Quantification of 277 miRNAs identified three up-regulated miRNAs and 18 down-regulated miRNAs in the spinal cords of DM-affected dogs. Based on gene ontology analysis, the target cluster of up-regulated miRNAs was associated with protein expression or modification and cellular response, and that of down-regulated miRNAs was associated with tissue development. In these clusters, we focused on the mechanism of protein ubiquitination. Polyubiquitination assay demonstrated that canine SOD1 proteins were polyubiquitinated and degraded by proteasomes. Immunohistochemistry of the spinal cords of DM-affected dogs showed that mutant SOD1 aggregations were not ubiquitin immunopositive. Using cultured cells, co-transfection of canine SOD1 and up-regulated miRNA in DM-affected dogs demonstrated that miR-23a, miR-142 and miR-221 significantly increased the proportion of cells with mutant SOD1 aggregation. These results suggested that up-regulated miRNAs in the spinal cords of DM-affected dogs may inhibit ubiquitination of misfolded SOD1 protein and induce mutant SOD1 aggregations, leading to further progression of degenerative processes in the DM pathology.

Canine SOD1 harboring E40K or T18S mutations promotes protein aggregation without reducing the global structural stability

Amyotrophic lateral sclerosis (ALS) is a progressive and fatal neurodegenerative disease associated with aggregation of superoxide dismutase 1 (SOD1) protein. More than 160 mutations in human SOD1 have been identified in familial ALS and extensively characterized in previous studies. Here, we investigated the effects of T18S and E40K mutations on protein aggregation of canine SOD1. These two mutations are exclusively found in canine degenerative myelopathy (an ALS-like neurodegenerative disease in dogs), whose phenotype is unknown at the level of protein folding. Interestingly, the T18S and E40K mutations did not alter far-UV CD spectrum, enzymatic activity, or global structural stability of canine SOD1. However, thioflavin-T assay and transmission electron microscopy analysis revealed that these mutations promote formation of fibrous aggregates, in particular in the Cu²⁺/Zn²⁺-unbound state. These evidence suggested that the T18S and E40K mutations promote protein aggregation through a unique mechanism, possibly involving destabilization of the local structure, reduction of net negative charge, or production of disulfide-linked oligomers.

Species-specific consequences of an E40K missense mutation in superoxide dismutase 1 (SOD1)

A glutamic acid to lysine (E40K) residue substitution in superoxide dismutase 1 (SOD1) is associated with canine degenerative myelopathy: the only naturally occurring large animal model of amyotrophic lateral sclerosis (ALS). The E40 residue is highly conserved across mammals, except the horse, which naturally carries the (dog mutant) K40 residue. Here we hypothesized that in vitro expression of mutant dog SOD1 would recapitulate features of human ALS (ie, SOD1 protein aggregation, reduced cell viability, perturbations in mitochondrial morphology and membrane potential, reduced ATP production, and increased superoxide ion levels); further, we hypothesized that an equivalent equine SOD1 variant would share similar perturbations in vitro, thereby explain horses' susceptibility to certain neurodegenerative diseases. As in human ALS, expression of mutant dog SOD1 was associated with statistically significant increased aggregate formation, raised superoxide levels (ROS), and altered mitochondrial morphology (increased branching (form factor)), when compared to wild-type dog SOD1-expressing cells. Similar deficits were not detected in cells expressing the equivalent horse SOD1 variant. Our data helps explain the ALS-associated cellular phenotype of dogs expressing the mutant SOD1 protein and reveals that species-specific sequence conservation does not necessarily predict pathogenicity. The work improves understanding of the etiopathogenesis of canine degenerative myelopathy.

Clinical, Pathological, and Ethical Considerations for the Conduct of Clinical Trials in Dogs with Naturally Occurring Cancer: A Comparative Approach to Accelerate Translational Drug Development

The role of comparative oncology in translational research is receiving increasing attention from drug developers and the greater biomedical research community. Pet dogs with spontaneous cancer are important and underutilized translational models, owing to dogs' large size and relative outbreeding, combined with their high incidence of certain tumor histotypes with significant biological, genetic, and histological similarities to their human tumor counterparts. Dogs with spontaneous tumors naturally develop therapy resistance and spontaneous metastasis, all in the context of an intact immune system. These fundamental features of cancer biology are often lacking in induced or genetically engineered preclinical tumor models and likely contribute to their poor predictive value and the associated overall high failure rate in oncology drug development. Thus, the conduct of clinical trials in pet dogs with naturally occurring cancer represents a viable surrogate and valuable intermediary step that should be increasingly incorporated into the cancer drug discovery and development pipeline. The development of molecular-targeted therapies has resulted in an expanded role of the pathologist in human oncology trials, and similarly the expertise of veterinary pathologists will be increasingly valuable to all phases of comparative oncology trial design and conduct. In this review, we provide a framework of clinical, ethical, and pathology-focused considerations for the increasing integration of translational research investigations in dogs with spontaneous cancer as a means to accelerate clinical cancer discovery and drug development.

In vitro evidence consistent with an interaction between wild-type and mutant SOD1 protein associated with canine degenerative myelopathy

Canine degenerative myelopathy (DM) is a progressive neurological disorder that may be considered to be a large animal model for specific forms of the fatal human disease, familial amyotrophic lateral sclerosis (fALS). DM is associated with a c118G>A mutation of the superoxide dismutase 1 (Sod1) gene, and a significant proportion of cases are inherited in an autosomal recessive manner in contrast to the largely, but not exclusively, dominant mode of inheritance in fALS. The consensus view is that these Sod1/SOD1 mutations result in a toxic gain of function but the mechanisms remain unclear. Here we used an in vitro neuroblastoma cell line transfection system to monitor wild-type and mutant forms of SOD1 fusion proteins containing either a Cherry or an enhanced green fluorescent protein (EGFP) tag. These fusion proteins retained SOD1 enzymatic activity on a native gel assay system. We demonstrate that SOD1 aggregate density is significantly higher in DM transfectants compared to wild-type. In addition, we show by co-immunoprecipitation and confocal microscopy, evidence for a potential interaction between wild-type and mutant forms of SOD1 in co-transfected cells. While in vitro studies have shown SOD1 heterodimer formation in fALS models, this is the first report for DM SOD1. Therefore, despite for the majority of cases there is a difference in the mode of inheritance between fALS and DM, a similar interaction between wild-type and mutant SOD1 forms can occur. Clarifying the role of SOD1 in DM may also be of benefit to understanding the role of SOD1 in fALS.

Plasma microRNA miR-26b as a potential diagnostic biomarker of degenerative myelopathy in Pembroke welsh corgis

BACKGROUND

Degenerative myelopathy (DM) is a progressive neurodegenerative disease frequently found in Pembroke Welsh Corgis (PWCs). Most DM-affected PWCs are homozygous for the mutant superoxide dismutase 1 (SOD1) allele; however, the genetic examination for the SOD1 mutation does not exclusively detect symptomatic dogs. In order to identify novel biomarkers, the plasma microRNA (miRNA) profiles of PWCs with DM were investigated.

RESULTS

Quantification of the plasma levels of 277 miRNAs by an RT-qPCR array identified 11 up-regulated miRNAs and 7 down-regulated miRNAs in DM-affected PWCs from those in wild-type SOD1 PWCs. A pathway analysis identified 3 miRNAs: miR-26b, miR-181a, and miR-196a, which potentially regulate several genes associated with SOD1. In order to validate the diagnostic accuracy of the candidate miRNAs in the aged PWC population, candidate miRNAs in plasma were measured by RT-qPCR and a receiver operating characteristic (ROC) curve analysis was performed. miR-26b had the largest area under the ROC curve for distinguishing DM PWCs from healthy PWCs (sensitivity, 66.7%; specificity, 87.0%). The plasma level of miR-26b was significantly higher in the DM group than in the healthy control group. A positive correlation was observed between increases in the plasma level of miR-26b and disease progression.

CONCLUSIONS

These results suggest that plasma miR-26b is a potential novel diagnostic biomarker of DM.

Revised Airlie House consensus guidelines for design and implementation of ALS clinical trials

OBJECTIVE

To revise the 1999 Airlie House consensus guidelines for the design and implementation of preclinical therapeutic studies and clinical trials in amyotrophic lateral sclerosis (ALS).

METHODS

A consensus committee comprising 140 key members of the international ALS community (ALS researchers, clinicians, patient representatives, research funding representatives, industry, and regulatory agencies) addressed 9 areas of need within ALS research: (1) preclinical studies; (2) biological and phenotypic heterogeneity; (3) outcome measures; (4) disease-modifying and symptomatic interventions; (5) recruitment and retention; (6) biomarkers; (7) clinical trial phases; (8) beyond traditional trial designs; and (9) statistical considerations. Assigned to 1 of 8 sections, committee members generated a draft set of guidelines based on a "background" of developing a (pre)clinical question and a "rationale" outlining the evidence and expert opinion. Following a 2-day, face-to-face workshop at the Airlie House Conference Center, a modified Delphi process was used to develop draft consensus research guidelines, which were subsequently reviewed and modified based on comments from the public. Statistical experts drafted a separate document of statistical considerations (section 9).

RESULTS

In this report, we summarize 112 guidelines and their associated backgrounds and rationales. The full list of guidelines, the statistical considerations, and a glossary of terms can be found in data available from Dryad (appendices e-3-e-5, doi.org/10.5061/dryad.32q9q5d). The authors prioritized 15 guidelines with the greatest potential to improve ALS clinical research.

CONCLUSION

The revised Airlie House ALS Clinical Trials Consensus Guidelines should serve to improve clinical trial design and accelerate the development of effective treatments for patients with ALS.

Protein disulphide isomerase is associated with mutant SOD1 in canine degenerative myelopathy

Canine degenerative myelopathy (DM) is a fatal neurodegenerative disorder prevalent in the canine population. It may represent a unique, naturally occurring disease model for human amyotrophic lateral sclerosis (ALS) because of similar clinical signs and association with superoxide dismutase 1 gene (SOD1) mutations. Misfolded SOD1 aggregates and endoplasmic reticulum (ER) stress are major pathophysiological features associated with ALS. Interestingly, an ER foldase, protein disulphide isomerase (PDI) is upregulated during ALS and it co-localizes with SOD1 inclusions in ALS patient tissues. Furthermore, mutations in the gene encoding PDI were recently associated with ALS. Given the genetic similarity between DM and ALS, we investigated whether ER stress and PDI were associated with DM. Protein extracts from spinal cord tissue of DM-affected dogs bearing a SOD1 mutation were examined for ER stress by western blotting. Immunohistochemical staining was also carried out to examine co-localization between endogenous PDI and SOD1 inclusions in spinal cord tissues of dogs affected with DM. PDI and CHOP, the proapoptotic protein induced during ER stress, were significantly upregulated in DM-affected dogs compared with controls. Furthermore, PDI co-localized with intracellular SOD1 aggregates in DM-affected dogs in all motor neurons examined, indicating that PDI may be a cellular defence mechanism against SOD1 misfolding in DM. Our results imply that ER stress is induced in DM-affected dogs; hence, it is a common pathological mechanism associated with both ALS and DM. The possibility that PDI may be a therapeutic target to inhibit SOD1 aggregation in DM dogs is also raised by this study.

Experimental models of focal and multifocal cerebral ischemia: a review

Rodent and rabbit stroke models have been instrumental in our current understanding of stroke pathophysiology; however, translational failure is a significant problem in preclinical ischemic stroke research today. There are a number of different focal cerebral ischemia models that vary in their utility, pathophysiology of causing disease, and their response to treatments. Unfortunately, despite active preclinical research using these models, treatment options for ischemic stroke have not significantly advanced since the food and drug administration approval of tissue plasminogen activator in 1996. This review aims to summarize current stroke therapies, the preclinical experimental models used to help develop stroke therapies, as well as their advantages and limitations. In addition, this review discusses the potential for naturally occurring canine ischemic stroke models to compliment current preclinical models and to help bridge the translational gap between small mammal models and human clinical trials.

Fisetin Exerts Antioxidant and Neuroprotective Effects in Multiple Mutant hSOD1 Models of Amyotrophic Lateral Sclerosis by Activating ERK

Oxidative stress exhibits a central role in the course of amyotrophic lateral sclerosis (ALS), a progressive neurodegenerative disease commonly found to include a copper/zinc superoxide dismutase (SOD1) gene mutation. Fisetin, a natural antioxidant, has shown benefits in varied neurodegenerative diseases. The possible effect of fisetin in ALS has not been clarified as of yet. We investigated whether fisetin affected mutant hSOD1 ALS models. Three different hSOD1-related mutant models were used: Drosophila expressing mutant hSOD1^G85R, hSOD1^G93A NSC34 cells, and transgenic mice. Fisetin treatment provided neuroprotection as demonstrated by an improved survival rate, attenuated motor impairment, reduced ROS damage and regulated redox homeostasis compared with those in controls. Furthermore, fisetin increased the expression of phosphorylated ERK and upregulated antioxidant factors, which were reversed by MEK/ERK inhibition. Finally, fisetin reduced the levels of both mutant and wild-type hSOD1 in vivo and in vitro, as well as the levels of detergent-insoluble hSOD1 proteins. The results indicate that fisetin protects cells from ROS damage and improves the pathological behaviors caused by oxidative stress in disease models related to SOD1 gene mutations probably by activating ERK, thereby providing a potential treatment for ALS.

Arginase-1 expressing microglia in close proximity to motor neurons were increased early in disease progression in canine degenerative myelopathy, a model of amyotrophic lateral sclerosis

Toxicity within superoxide dismutase-1 (SOD1)-associated familial amyotrophic lateral sclerosis (ALS) is non-cell autonomous with direct contribution from microglia. Microglia exhibit variable expression of neuroprotective and neurotoxic molecules throughout disease progression. The mechanisms regulating microglial phenotype within ALS are not well understood. This work presents a first study to examine the specific microglial phenotypic response in close association to motor neurons in a naturally occurring disease model of ALS, canine degenerative myelopathy (DM). Microglia closely associated with motor neurons were increased in all stages of DM progression, although only DM Late reached statistical significance. Furthermore, the number of arginase-1 expressing microglia per motor neuron were significantly increased in early stages of DM, whereas the number of inducible nitric oxide synthase (iNOS)-expressing microglia per motor neuron was indistinguishable from aged controls at all stages of disease. Fractalkine, a chemotactic molecule for microglia, was expressed in motor neurons, and the fractalkine receptor was specifically localized to microglia. However, we found no correlation between microglial response and lumbar spinal cord fractalkine levels. Taken together, these data suggest that arginase-1-expressing microglia are recruited to the motor neuron early in DM disease through a fractalkine-independent mechanism.

The Effects of Various Weather Conditions as a Potential Ischemic Stroke Trigger in Dogs

Stroke is the fifth leading cause of death in the United States, and is the leading cause of serious, long-term disability worldwide. There are at least 795,000 new or recurrent strokes each year, and approximately 85% of all stroke occurrences are ischemic. Unfortunately, companion animals are also at risk for ischemic stroke. Although the exact incidence of ischemic stroke in companion animals is unknown, some studies, and the veterinary information network (VIN), report that approximately 3% of neurological case referrals are due to a stroke. There is a long list of predisposing factors associated with the risk of ischemic stroke in both humans and canines; however, these factors do not explain why a stroke happens at a particular time on a particular day. Our understanding of these potential stroke “triggers” is limited, and the effect of transient environmental exposures may be one such “trigger”. The present study investigated the extent to which the natural occurrence of canine ischemic stroke was related to the weather conditions in the time-period immediately preceding the onset of stroke. The results of the present study demonstrated that the change in weather conditions could be a potential stroke trigger, with the strokes evaluated occurring after periods of rapid, large fluctuations in weather conditions. There are currently no epidemiological data on the seasonal variability of ischemic stroke in dogs, and determining whether canine stroke parallels human stroke would further validate the use of companion dogs as an appropriate naturally occurring model.

Biological Spectrum of Amyotrophic Lateral Sclerosis Prions

Amyotrophic lateral sclerosis (ALS) and frontotemporal lobar dementia (FTLD) are two neurodegenerative diseases with distinct clinical features but common genetic causes and neuropathological signatures. Ten years after the RNA-binding protein TDP-43 was discovered as the main protein in the cytoplasmic inclusions that characterize ALS and FTLD, their pathogenic mechanisms have never seemed more complex. Indeed, discoveries of the past decade have revolutionized our understanding of these diseases, highlighting their genetic heterogeneity and the involvement of protein-RNA assemblies in their pathogenesis. Importantly, these assemblies serve as the foci of protein misfolding and mature into insoluble structures, which further recruit native proteins, turning them into misfolded forms. This self-perpetuating mechanism is a twisted version of classical prion replication that leads to amplification of pathological protein complexes that spread throughout the neuraxis, offering a pathogenic principle that underlies the rapid disease progression that characterizes ALS and FTLD.

Human SOD1 ALS Mutations in a Drosophila Knock-In Model Cause Severe Phenotypes and Reveal Dosage-Sensitive Gain- and Loss-of-Function Components

Amyotrophic Lateral Sclerosis (ALS) is the most common adult-onset motor neuron disease and familial forms can be caused by numerous dominant mutations of the copper-zinc superoxide dismutase 1 (SOD1) gene. Substantial efforts have been invested in studying SOD1-ALS transgenic animal models; yet, the molecular mechanisms by which ALS-mutant SOD1 protein acquires toxicity are not well understood. ALS-like phenotypes in animal models are highly dependent on transgene dosage. Thus, issues of whether the ALS-like phenotypes of these models stem from overexpression of mutant alleles or from aspects of the SOD1 mutation itself are not easily deconvolved. To address concerns about levels of mutant SOD1 in disease pathogenesis, we have genetically engineered four human ALS-causing SOD1 point mutations (G37R, H48R, H71Y, and G85R) into the endogenous locus of Drosophila SOD1 (dsod) via ends-out homologous recombination and analyzed the resulting molecular, biochemical, and behavioral phenotypes. Contrary to previous transgenic models, we have recapitulated ALS-like phenotypes without overexpression of the mutant protein. Drosophila carrying homozygous mutations rendering SOD1 protein enzymatically inactive (G85R, H48R, and H71Y) exhibited neurodegeneration, locomotor deficits, and shortened life span. The mutation retaining enzymatic activity (G37R) was phenotypically indistinguishable from controls. While the observed mutant dsod phenotypes were recessive, a gain-of-function component was uncovered through dosage studies and comparisons with age-matched dsod null animals, which failed to show severe locomotor defects or nerve degeneration. We conclude that the Drosophila knock-in model captures important aspects of human SOD1-based ALS and provides a powerful and useful tool for further genetic studies.

Erythrocyte copper chaperone for superoxide dismutase and superoxide dismutase as biomarkers for hepatic copper concentrations in Labrador retrievers

Hereditary hepatic copper accumulation in Labrador retrievers leads to hepatitis with fibrosis and eventually cirrhosis. The development of a non-invasive blood-based biomarker for copper status in dogs could be helpful in identifying dogs at risk and to monitor copper concentrations during treatment. In this study, two cellular copper metabolism proteins, Cu/Zn superoxide dismutase (SOD1) and its chaperone (copper chaperone for SOD1, CCS) were measured in erythrocytes and tested for association with hepatic copper concentrations in 15 Labrador retrievers with normal or increased hepatic copper concentrations. Antibodies against CCS and SOD1 were applicable for use in canine specimens. This was demonstrated by the loss of immune-reactive bands for CCS and SOD1 in siRNA treated canine bile duct epithelial cells. Erythrocyte CCS and CCS/SOD1 ratios were decreased 2.37 (P <0.001) and 3.29 (P <0.001) fold in the high copper group compared to the normal copper group. Erythrocyte CCS and CCS/SOD1 ratio are potential new biomarkers for hepatic copper concentrations in Labrador retrievers and could facilitate early diagnosis and treatment monitoring for copper-associated hepatitis in dogs.

Variants within the SP110 nuclear body protein modify risk of canine degenerative myelopathy

Canine degenerative myelopathy (DM) is a naturally occurring neurodegenerative disease with similarities to some forms of amyotrophic lateral sclerosis (ALS). Most dogs that develop DM are homozygous for a common superoxide dismutase 1 gene (SOD1) mutation. However, not all dogs homozygous for this mutation develop disease. We performed a genome-wide association analysis in the Pembroke Welsh Corgi (PWC) breed comparing DM-affected and -unaffected dogs homozygous for the SOD1 mutation. The analysis revealed a modifier locus on canine chromosome 25. A haplotype within the SP110 nuclear body protein (SP110) was present in 40% of affected compared with 4% of unaffected dogs (P = 1.5 × 10(-5)), and was associated with increased probability of developing DM (P = 4.8 × 10(-6)) and earlier onset of disease (P = 1.7 × 10(-5)). SP110 is a nuclear body protein involved in the regulation of gene transcription. Our findings suggest that variations in SP110-mediated gene transcription may underlie, at least in part, the variability in risk for developing DM among PWCs that are homozygous for the disease-related SOD1 mutation. Further studies are warranted to clarify the effect of this modifier across dog breeds.

A look into the future of ALS research

Although amyotrophic lateral sclerosis (ALS), also referred as 'Lou Gehrig's Disease,' was first described in 1869 and the first disease-associated gene was discovered almost 20 years ago, the disease etiology is still not fully understood and treatment options are limited to one drug approved by the US Food and Drug Administration (FDA). The slow translational progress suggests that current research models are not ideal to study such a complicated disease and need to be re-examined. Progress will require greater insight into human genes and biology involved in ALS susceptibility, as well as a deeper understanding of disease phenotype at the histological and molecular levels. Improving human disease outcome will require directing focus toward improved assessment technologies and innovative approaches.

A retrospective study of the prevalence of the canine degenerative myelopathy associated superoxide dismutase 1 mutation (SOD1:c.118G > A) in a referral population of German Shepherd dogs from the UK

BACKGROUND

Canine degenerative myelopathy (CDM) is an adult onset, progressive neurodegenerative disease of the spinal cord. The disease was originally described in the German Shepherd dog (GSD), but it is now known to occur in many other dog breeds. A previous study has identified a mutation in the superoxide dismutase 1 gene (SOD1:c.118G > A) that is associated with susceptibility to CDM. In the present study, restriction fragment length polymorphism (RFLP) analysis was used to genotype GSD for SOD1:c.118G > A in order to estimate the prevalence of the mutation in a referral population of GSD in the UK.

RESULTS

This study demonstrated that the RFLP assay, based on use of PCR and subsequent digestion with the Eco571 enzyme, provided a simple genotyping test for the SOD1:c.118G > A mutation. In a young GSD population (i.e. dogs less than 6 years of age, before clinical signs of the disease usually become apparent), 8 of 50 dogs were found to be homozygous and a further 19 were heterozygous for the mutation. In dogs over 8 years of age, 21 of 50 dogs admitted to a tertiary referral hospital with pelvic limb ataxia as a major clinical sign were homozygous for the mutation, compared to none of 50 dogs of similar age, but where no neurological disease was reported on referral.

CONCLUSIONS

This data suggests that genotyping for the SOD1:c.118G > A mutation is clinically applicable and that the mutation has a high degree of penetrance. Genotyping might also be useful for screening the GSD population to avoid mating of two carriers, but since the allele frequency is relatively high in the UK population of GSD, care should be taken to avoid reduction in genetic diversity within the breed.

Breed distribution of SOD1 alleles previously associated with canine degenerative myelopathy

Background

Previous reports associated 2 mutant SOD1 alleles (SOD1:c.118A and SOD1:c.52T) with degenerative myelopathy in 6 canine breeds. The distribution of these alleles in other breeds has not been reported.

Objective

To describe the distribution of SOD1:c.118A and SOD1:c.52T in 222 breeds.

Animals

DNA from 33,747 dogs was genotyped at SOD1:c.118,SOD1:c.52, or both. Spinal cord sections from 249 of these dogs were examined.

Methods

Retrospective analysis of 35,359 previously determined genotypes at SOD1:c.118G>A or SOD1:c.52A>T and prospective survey to update the clinical status of a subset of dogs from which samples were obtained with a relatively low ascertainment bias.

Results

The SOD1:c.118A allele was found in cross‐bred dogs and in 124 different canine breeds whereas the SOD1:c.52T allele was only found in Bernese Mountain Dogs. Most of the dogs with histopathologically confirmed degenerative myelopathy were SOD1:c.118A homozygotes, but 8 dogs with histopathologically confirmed degenerative myelopathy were SOD1:c.118A/G heterozygotes and had no other sequence variants in their SOD1 amino acid coding regions. The updated clinical conditions of dogs from which samples were obtained with a relatively low ascertainment bias suggest that SOD1:c.118A homozygotes are at a much higher risk of developing degenerative myelopathy than are SOD1:c.118A/G heterozygotes.

Conclusions and Clinical Importance

We conclude that the SOD1:c.118A allele is widespread and common among privately owned dogs whereas the SOD1:c.52T allele is rare and appears to be limited to Bernese Mountain Dogs. We also conclude that breeding to avoid the production of SOD1:c.118A homozygotes is a rational strategy.