Common molecular signature in SOD1 for both sporadic and familial amyotrophic lateral sclerosis

Cu, Zn-superoxide dismutase 1 (SOD1) is a novel target of Puromycin-sensitive aminopeptidase (PSA/NPEPPS): PSA/NPEPPS is a possible modifier of amyotrophic lateral sclerosis

Accumulation of misfolded neurotoxic Cu, Zn-superoxide dismutase-1 (SOD1) protein found in both familial and sporadic amyotrophic lateral sclerosis (ALS) is recognized as an important contributing factor of neuronal cell death. However, little is known about the mechanisms controlling the accumulation and turnover of SOD1 protein. Puromycin-sensitive aminopeptidase (PSA/NPEPPS) was recently identified as a major peptidase acting on neurotoxic TAU protein and protecting against TAU-induced neurodegeneration. In addition, recent report implicated PSA/NPEPPS in the direct removal of neurotoxic polyglutamine repeats. These combined data suggest that PSA/NPEPPS might represent a novel degradation pathway targeting pathologically aggregating neurotoxic protein substrates including SOD1. Here, we report that PSA/NPEPPS directly regulates SOD1 protein abundance and clearance via proteolysis. In addition, PSA/NPEPPS expression is significantly decreased in motor neurons of both SOD^G93A transgenic mice and sporadic ALS patients, suggesting its possible contribution to the disease pathogenesis. These results implicate SOD1 as a new target protein of PSA/NPEPPS and point to the possible neuroprotective role of PSA/NPEPPS in ALS.

SOD1 Transcriptional and Posttranscriptional Regulation and Its Potential Implications in ALS

Copper-zinc superoxide dismutase (SOD1) is a detoxifying enzyme localized in the cytosol, nucleus, peroxisomes, and mitochondria. The discovery that mutations in SOD1 gene cause a subset of familial amyotrophic lateral sclerosis (FALS) has attracted great attention, and studies to date have been mainly focused on discovering mutations in the coding region and investigation at protein level. Considering that changes in SOD1 mRNA levels have been associated with sporadic ALS (SALS), a molecular understanding of the processes involved in the regulation of SOD1 gene expression could not only unravel novel regulatory pathways that may govern cellular phenotypes and changes in diseases but also might reveal therapeutic targets and treatments. This review seeks to provide an overview of SOD1 gene structure and of the processes through which SOD1 transcription is controlled. Furthermore, we emphasize the importance to focus future researches on investigating posttranscriptional mechanisms and their relevance to ALS.

In Vivo imaging reveals distinct inflammatory activity of CNS microglia versus PNS macrophages in a mouse model for ALS

Mutations in the enzyme superoxide dismutase-1 (SOD1) cause hereditary variants of the fatal motor neuronal disease Amyotrophic lateral sclerosis (ALS). Pathophysiology of the disease is non-cell-autonomous: neurotoxicity is derived not only from mutant motor neurons but also from mutant neighbouring non-neuronal cells. In vivo imaging by two-photon laser-scanning microscopy was used to compare the role of microglia/macrophage-related neuroinflammation in the CNS and PNS using ALS-linked transgenic SOD1^G93A mice. These mice contained labeled projection neurons and labeled microglia/macrophages. In the affected lateral spinal cord (in contrast to non-affected dorsal columns), different phases of microglia-mediated inflammation were observed: highly reactive microglial cells in preclinical stages (in 60-day-old mice the reaction to axonal transection was ∼180% of control) and morphologically transformed microglia that have lost their function of tissue surveillance and injury-directed response in clinical stages (reaction to axonal transection was lower than 50% of control). Furthermore, unlike CNS microglia, macrophages of the PNS lack any substantial morphological reaction while preclinical degeneration of peripheral motor axons and neuromuscular junctions was observed. We present in vivo evidence for a different inflammatory activity of microglia and macrophages: an aberrant neuroinflammatory response of microglia in the CNS and an apparently mainly neurodegenerative process in the PNS.

Generalization of the prion hypothesis to other neurodegenerative diseases: an imperfect fit

Protein misfolding diseases have been classically understood as diffuse errors in protein folding, with misfolded protein arising autonomously throughout a tissue due to a pathologic stressor. The field of prion science has provided an alternative mechanism whereby a seed of pathologically misfolded protein, arising exogenously or through a rare endogenous structural fluctuation, yields a template to catalyze misfolding of the native protein. The misfolded protein may then spread intercellularly to communicate the misfold to adjacent areas and ultimately infect a whole tissue. Mounting evidence implicates a prion-like process in the propagation of several neurodegenerative diseases, including Alzheimer's, Parkinson's, Huntington's, amyotrophic lateral sclerosis, and the tauopathies. However, the parallels between the events observed in these conditions and those in prion disease are often incomplete. The aim of this review was to examine the current state of knowledge concerning the mechanisms of protein misfolding and aggregation for neurodegeneration-associated proteins. In addition, possible methods of intercellular spread are described that focus on the hypothesis that released microvesicles function as misfolded protein delivery vehicles, and the therapeutic options enabled by viewing these diseases from the prion perspective.

IL-17A is increased in the serum and in spinal cord CD8 and mast cells of ALS patients

The contribution of inflammation to neurodegenerative diseases is increasingly recognized, but the role of inflammation in sporadic amyotrophic lateral sclerosis (sALS) is not well understood and no animal model is available. We used enzyme-linked immunosorbent assays (ELISAs) to measure the cytokine interleukin-17A (IL-17A) in the serum of ALS patients (n = 32; 28 sporadic ALS (sALS) and 4 familial ALS (fALS)) and control subjects (n = 14; 10 healthy subjects and 4 with autoimmune disorders). IL-17A serum concentrations were 5767 ± 2700 pg/ml (mean ± SEM) in sALS patients and 937 ± 927 pg/ml in fALS patients in comparison to 7 ± 2 pg/ml in control subjects without autoimmune disorders (p = 0.008 ALS patients vs. control subjects by Mann-Whitney test). Sixty-four percent of patients and no control subjects had IL-17A serum concentrations > 50 pg/ml (p = 0.003 ALS patients vs. healthy subjects by Fisher's exact test). The spinal cords of sALS (n = 8), but not control subjects (n = 4), were infiltrated by interleukin-1β- (IL-1β-), and tumor necrosis factor-α-positive macrophages (co-localizing with neurons), IL-17A-positive CD8 cells, and IL-17A-positive mast cells. Mononuclear cells treated with aggregated forms of wild type superoxide dismutase-1 (SOD-1) showed induction of the cytokines IL-1β, interleukin-6 (IL-6), and interleukin-23 (IL-23) that may be responsible for induction of IL-17A. In a microarray analysis of 28,869 genes, stimulation of peripheral blood mononuclear cells by mutant superoxide dismutase-1 induced four-fold higher transcripts of interleukin-1α (IL-1α), IL-6, CCL20, matrix metallopeptidase 1, and tissue factor pathway inhibitor 2 in mononuclear cells of patients as compared to controls, whereas the anti-inflammatory cytokine interleukin-10 (IL-10) was increased in mononuclear cells of control subjects. Aggregated wild type SOD-1 in sALS neurons could induce in mononuclear cells the cytokines inducing chronic inflammation in sALS spinal cord, in particular IL-6 and IL-17A, damaging neurons. Immune modulation of chronic inflammation may be a new approach to sALS.

Amyotrophic lateral sclerosis: applications of stem cells - an update

Neurodegenerative diseases are a growing public health challenge, and amyotrophic lateral sclerosis (ALS) remains a fatal incurable disease. The advent of stem cell therapy has opened new horizons for both researchers and ALS patients, desperately looking for a treatment. ALS must be considered a systemic disease affecting many cell phenotypes besides motor neurons, even outside the central nervous system. Cell replacement therapy needs to address the specific neurobiological issues of ALS to safely and efficiently reach clinical settings. Moreover, the enormous potential of induced pluripotent cells directly derived from patients for modeling and understanding the pathological mechanisms, in correlation with the discoveries of new genes and animal models, provides new opportunities that need to be integrated with previously described transplantation strategies. Finally, a careful evaluation of preclinical data in conjunction with wary patient choice in clinical trials needs to be established in order to generate meaningful results.

Nonamyloid aggregates arising from mature copper/zinc superoxide dismutases resemble those observed in amyotrophic lateral sclerosis

Protein aggregation is a hallmark of many diseases, including amyotrophic lateral sclerosis (ALS) where aggregation of copper/zinc superoxide dismutase (SOD1) is implicated in pathogenesis. We report here that fully metallated (holo) SOD1 under physiologically relevant solution conditions can undergo changes in metallation and/or dimerization over time and form aggregates that do not exhibit classical characteristics of amyloid. The relevance of the observed aggregation to disease is demonstrated by structural and tinctorial analyses, including the novel observation of binding of an anti-SOD1 antibody that specifically recognizes aggregates in ALS patients and mice models. ALS-associated SOD1 mutations can promote aggregation but are not essential. The SOD1 aggregation is characterized by a lag phase, which is diminished by self- or cross-seeding and by heterogeneous nucleation. We interpret these findings in terms of an expanded aggregation mechanism consistent with other in vitro and in vivo findings that point to multiple pathways for the formation of toxic aggregates by different forms of SOD1.

Carbonic anhydrase I is recognized by an SOD1 antibody upon biotinylation of human spinal cord extracts

We recently reported the presence of a novel 32 kDa protein immunoreactive to a copper, zinc superoxide dismutase (SOD1) antibody within the spinal cord of patients with amyotrophic lateral sclerosis (ALS). This unique protein species was generated by biotinylation of spinal cord tissue extracts to detect conformational changes of SOD1 specific to ALS patients. To further characterize this protein, we enriched the protein by column chromatography and determined its protein identity by mass spectrometry. The protein that gave rise to the 32 kDa species upon biotinylation was identified as carbonic anhydrase I (CA I). Biotinylation of CA I from ALS spinal cord resulted in the generation of a novel epitope recognized by the SOD1 antibody. This epitope could also be generated by biotinylation of extracts from cultured cells expressing human CA I. Peptide competition assays identified the amino acid sequence in carbonic anhydrase I responsible for binding the SOD1 antibody. We conclude that chemical modifications used to identify pathogenic protein conformations can lead to the identification of unanticipated proteins that may participate in disease pathogenesis.

Astrocyte loss of mutant SOD1 delays ALS disease onset and progression in G85R transgenic mice

Approximately 10% of patients with amyotrophic lateral sclerosis (ALS) have familial ALS (FALS), and 20% of FALS are caused by mutations of superoxide dismutase type 1 (MTSOD1). The fact that some MTSOD1s that cause FALS have full dismutase activity (e.g. G37R) and others no dismutase activity (e.g. G85R) suggests that MTSOD1 causes FALS due to toxicity of the protein rather than a loss in enzymatic function. Compelling data have demonstrated that motor neuron (MN) degeneration can result from a non-cell autonomous effect of the MTSOD1. In order to clarify the role of astrocytes in FALS, we deleted MTSOD1 in astrocytes of G85R transgenic mice. In contrast to a similar study using G37R mice in which astrocyte MTSOD1 loss affected only the late phase of ALS disease, we found that astrocyte MTSOD1 loss in G85R mice delayed disease onset and prolonged the early phase of disease progression, without affecting the late phase. In addition, astrocyte G85R knockdown resulted in decreased microgliosis, decreased SOD1-immunoreactive inclusions and preservation of GLT-1 transporter expression. The differential effects of astrocyte G85R versus G37R knockdown on MN death demonstrate SOD1 mutation-specific effects on ALS pathogenesis; these differences may be a result of the different dismutase activities of the two mutants. The effect of the knockdown of G85R expression in astrocytes on onset as well as disease duration highlights the importance of this cell type in FALS.

Wild-type and mutant SOD1 share an aberrant conformation and a common pathogenic pathway in ALS

Many mutations confer upon copper/zinc superoxide dismutase-1 (SOD1) one or more toxic function(s) that impair motor neuron viability and cause familial amyotrophic lateral sclerosis (FALS). Using a conformation-specific antibody that detects misfolded SOD1 (C4F6), we demonstrate that oxidized WT-SOD1 and mutant-SOD1 share a conformational epitope that is not present in normal WT-SOD1. In a subset of human sporadic ALS (SALS) cases, motor neurons in the lumbosacral spinal cord displayed striking C4F6 immunoreactivity, denoting the presence of aberrant WT-SOD1 species. Recombinant, oxidized WT-SOD1 and WT-SOD1 immunopurified from SALS tissues inhibited kinesin-based fast axonal transport in a manner similar to FALS-linked mutant SOD1. Studies here suggest that WT-SOD1 can be pathogenic in SALS and identifies an SOD1-dependent pathogenic mechanism common to FALS and SALS.

A ditryptophan cross-link is responsible for the covalent dimerization of human superoxide dismutase 1 during its bicarbonate-dependent peroxidase activity

Unlike intermolecular disulfide bonds, other protein cross-links arising from oxidative modifications cannot be reversed and are presumably more toxic to cells because they may accumulate and induce protein aggregation. However, most of these irreversible protein cross-links remain poorly characterized. For instance, the antioxidant enzyme human superoxide dismutase 1 (hSod1) has been reported to undergo non-disulfide covalent dimerization and further oligomerization during its bicarbonate-dependent peroxidase activity. The dimerization was shown to be dependent on the oxidation of the single, solvent-exposed Trp(32) residue of hSod1, but the covalent dimer was not isolated nor was its structure determined. In this work, the hSod1 covalent dimer was isolated, digested with trypsin in H(2)O and H(2)(18)O, and analyzed by UV-Vis spectroscopy and mass spectrometry (MS). The results demonstrate that the covalent dimer consists of two hSod1 subunits cross-linked by a ditryptophan, which contains a bond between C3 and N1 of the respective Trp(32) residues. We further demonstrate that the cross-link cleaves under usual MS/MS conditions leading to apparently unmodified Trp(32), partially hinders proteolysis, and provides a mechanism to explain the formation of hSod1 covalent trimers and tetramers. This characterization of the covalent hSod1 dimer identifies a novel oxidative modification of protein Trp residues and provides clues for studying its occurrence in vivo.

DNA-triggered aggregation of copper, zinc superoxide dismutase in the presence of ascorbate

The oxidative damage hypothesis proposed for the function gain of copper, zinc superoxide dismutase (SOD1) maintains that both mutant and wild-type (WT) SOD1 catalyze reactions with abnormal substrates that damage cellular components critical for viability of the affected cells. However, whether the oxidative damage of SOD1 is involved in the formation of aggregates rich in SOD1 or not remains elusive. Here, we sought to explore the oxidative aggregation of WT SOD1 exposed to environments containing both ascorbate (Asc) and DNA under neutral conditions. The results showed that the WT SOD1 protein was oxidized in the presence of Asc. The oxidation results in the higher affinity of the modified protein for DNA than that of the unmodified protein. The oxidized SOD1 was observed to be more prone to aggregation than the WT SOD1, and the addition of DNA can significantly accelerate the oxidative aggregation. Moreover, a reasonable relationship can be found between the oxidation, increased hydrophobicity, and aggregation of SOD1 in the presence of DNA. The crucial step in aggregation is neutralization of the positive charges on some SOD1 surfaces by DNA binding. This study might be crucial for understanding molecular forces driving the protein aggregation.

Microglia in ALS: the good, the bad, and the resting

Inflammation, including microglial activation and T cell infiltration, is a neuropathological hallmark of amyotrophic lateral sclerosis (ALS), a rapidly progressing neurodegenerative disease. The identification of mutations in the gene for Cu2+/Zn2+ superoxide dismutase (SOD1) from patients with an inherited form of ALS enabled the creation of transgenic mice overexpressing mutant forms of SOD1 (mSOD1) which develop a motoneuron disease that resembles the disease seen in ALS patients. These transgenic mice display similar inflammatory reactions at sites of motoneuron injury as detected in ALS patients, enabling the observation that this inflammation is not simply a late consequence of motoneuron degeneration, but actively contributes to the balance between neuroprotection and neurotoxicity. The microglial and T cell activation states influence the rate of disease progression. Initially, microglia and T cells can slow disease progression, while they may later contribute to the acceleration of disease. Accumulation of intracellular and extracellular misfolded mSOD1 may be key events regulating the transformation from neuroprotective alternatively activated M2 microglia to cytotoxic classically activated M1 microglia. Intracellular and extracellular mSOD1 utilizing different pathways may enhance the production and release of reactive oxygen species (ROS) and augment the inflammatory cytokine cascade from microglia. These ROS and cytokines may increase the susceptibility of motoneurons to glutamate toxicity and inhibit the function and expression of astrocytic glutamate transporters resulting in further neurotoxicity. Thus, the cumulative evidence suggests that inflammation plays a central role in ALS and manipulating these microglial effector functions may potentially modify the outcome of this devastating disease.

Novel antibodies reveal inclusions containing non-native SOD1 in sporadic ALS patients

Mutations in CuZn-superoxide dismutase (SOD1) cause amyotrophic lateral sclerosis (ALS) and are found in 6% of ALS patients. Non-native and aggregation-prone forms of mutant SOD1s are thought to trigger the disease. Two sets of novel antibodies, raised in rabbits and chicken, against peptides spaced along the human SOD1 sequence, were by enzyme-linked immunosorbent assay and an immunocapture method shown to be specific for denatured SOD1. These were used to examine SOD1 in spinal cords of ALS patients lacking mutations in the enzyme. Small granular SOD1-immunoreactive inclusions were found in spinal motoneurons of all 37 sporadic and familial ALS patients studied, but only sparsely in 3 of 28 neurodegenerative and 2 of 19 non-neurological control patients. The granular inclusions were by confocal microscopy found to partly colocalize with markers for lysosomes but not with inclusions containing TAR DNA binding protein-43, ubiquitin or markers for endoplasmic reticulum, autophagosomes or mitochondria. Granular inclusions were also found in carriers of SOD1 mutations and in spinobulbar muscular atrophy (SBMA) patients and they were the major type of inclusion detected in ALS patients homozygous for the wild type-like D90A mutation. The findings suggest that SOD1 may be involved in ALS pathogenesis in patients lacking mutations in the enzyme.

Wild-type human SOD1 overexpression does not accelerate motor neuron disease in mice expressing murine Sod1 G86R

Approximately 10% of the cases of amyotrophic lateral sclerosis (ALS) are inherited, with the majority of identified linkages in the gene encoding Cu/Zn superoxide dismutase (SOD1). Recent studies showed that human wild-type SOD1 (SOD1(WT)) overexpression accelerated disease in mice expressing human SOD1 mutants linked to ALS. However, there is a controversy whether the exacerbation mechanism occurs through coaggregation of human SOD1(WT) with SOD1 mutants, stabilization by SOD1(WT) of toxic soluble SOD1 species, or conversion of SOD1(WT) into toxic species through oxidative damage. To further address whether the exacerbation of disease requires misfolding, modifications, and/or interaction of SOD1(WT) with pathogenic forms of SOD1 species, we have studied the effect of human SOD1(WT) overexpression in mice expressing the murine mutant Sod1(G86R). Surprisingly, unlike a previous report with SOD1(G85R) mice, SOD1(WT) overexpression did not affect the life span of Sod1(G86R) mice. Our analysis of spinal cord extracts revealed a lack of heterodimerization or aggregation between human SOD1(WT) and mouse Sod1(G86R) proteins. Moreover, there was no evidence of conversion of SOD1(WT) into misfolded or abnormal SOD1 isoforms based on immunoreactivity with monoclonal antibodies specific to misfolded forms of SOD1 mutants and on analysis of SOD1 isoforms after two-dimensional gel electrophoresis. We conclude that a direct interaction between wild type and mutant forms of SOD1 is required for exacerbation of ALS disease by SOD1(WT) protein.

SOD1 mRNA expression in sporadic amyotrophic lateral sclerosis

The mutated Cu,Zn-superoxide dismutase gene (SOD1) (E.C. No. 1.15.1.1) is generally recognized as a pathological cause of 20% of the familial form of Amyotrophic Lateral Sclerosis (ALS). However, several pieces of evidence also show that wild-type SOD1, under conditions of cellular stress, is implicated in a significant fraction of sporadic ALS cases, which represent 90% of ALS patients. Herein, we describe an abnormally high level of SOD1 transcript in spinal cord, brain stem and lymphocytes of sporadic ALS patients. Protein expression studies show a similar or lower amount of SOD1 in affected brain areas and lymphocytes, respectively. No differences are found in brain regions (cerebellum and non-motor cerebral cortex) not involved in the ALS neurodegenerative processes. In this report, cell and disease specificity are shown since no mRNA SOD1 increase is observed in sporadic ALS fibroblasts or in lymphocytes of patients affected by Alzheimer's disease. These findings provide new insight and understanding of the pathologic causes of sporadic forms of ALS and allow a possible explanation for the molecular involvement of wild-type SOD1.

Measures of bulbar and spinal motor function, muscle innervation, and mitochondrial function in ALS rats

Symptom onset in amyotrophic lateral sclerosis (ALS) may occur in the muscles of the limbs (spinal onset) or those of the head and neck (bulbar onset). Most preclinical studies have focused on spinal symptoms, despite the prevalence of and increased morbidity and mortality associated with bulbar disease. We measured lick rhythm and tongue force to evaluate bulbar disease in the SOD1-G93A rat model of familial ALS. Body weight and grip strength were measured concomitantly. Testing spanned the early (maturation), middle (pre-symptomatic), and late (symptomatic and end-stage) phases of the disease. We measured a persistent tongue motility deficit that became apparent in the early phase of the disease, providing behavioral evidence of bulbar pathology. At end-stage, however, cytochrome oxidase (CO) activity was normal in the hypoglossal nucleus, and in the tongue, neuromuscular innervation, citrate synthase (CS) protein levels and activity, and uncoupling protein 3 (UCP3) protein levels remained unchanged. Interestingly, significant denervation and atrophy were evident in the end-stage sternomastoid muscle, providing peripheral anatomical evidence of bulbar pathology. Changes in body weight and grip strength occurred in the late phase of the disease. Extensive atrophy and denervation were observed in the end-stage gastrocnemius muscle. In contrast to our findings in the tongue, CS protein levels were decreased in the extensor digitorum longus (EDL) and soleus, although CS activity was maintained or increased. UCP3 protein was decreased also in the EDL. These data provide evidence of differential effects in muscles that were more or less affected by disease.

Extracellular mutant SOD1 induces microglial-mediated motoneuron injury

Through undefined mechanisms, dominant mutations in (Cu/Zn) superoxide dismutase-1 (mSOD1) cause the non-cell-autonomous death of motoneurons in inherited amyotrophic lateral sclerosis (ALS). Microgliosis at sites of motoneuron injury is a neuropathological hallmark of ALS. Extracellular mutant SOD1 (mSOD1) causes motoneuron injury and triggers microgliosis in spinal cord cultures, but it is unclear whether the injury results from extracellular mSOD1 directly interacting with motoneurons or is mediated through mSOD1-activated microglia. To dissociate these potential mSOD1-mediated neurotoxic mechanisms, the effects of extracellular human mSOD1(G93A) or mSOD1(G85R) were assayed using primary cultures of motoneurons and microglia. The data demonstrate that exogenous mSOD1(G93A) did not cause detectable direct killing of motoneurons. In contrast, mSOD1(G93A) or mSOD1(G85R) did induce the morphological and functional activation of microglia, increasing their release of pro-inflammatory cytokines and free radicals. Furthermore, only when microglia was co-cultured with motoneurons did extracellular mSOD1(G93A) injure motoneurons. The microglial activation mediated by mSOD1(G93A) was attenuated using toll-like receptors (TLR) 2, TLR4 and CD14 blocking antibodies, or when microglia lacked CD14 expression. These data suggest that extracellular mSOD1(G93A) is not directly toxic to motoneurons but requires microglial activation for toxicity, utilizing CD14 and TLR pathways. This link between mSOD1 and innate immunity may offer novel therapeutic targets in ALS.

Mutant SOD1 knockdown in all cell types ameliorates disease in G85R SOD1 mice with a limited additional effect over knockdown restricted to motor neurons

Approximately 10% of patients with amyotrophic lateral sclerosis (ALS) have familial ALS (FALS), and 20% of FALS is caused by mutant Cu/Zn superoxide dismutase type 1 (MTSOD1). Previous studies have convincingly demonstrated that MTSOD1 expression in other cell types besides motor neurons (MNs) contributes to disease in MTSOD1 FALS transgenic mice. Using Cre/LoxP methods, we knocked down G85R SOD1 mRNA by 66% in all cell types in 3-month-old FALS transgenic mice, delaying disease onset and lengthening disease duration. Surprisingly, the effect on onset and early disease duration was similar to that seen in FALS transgenic mice with approximately 25% knockdown prenatally in G85R SOD1 mRNA restricted to MNs and some interneurons. These results demonstrate no clear cumulative effect on disease onset or early disease duration from knocking down G85R SOD1 in other cell types in addition to MNs/interneurons; the findings bring up the possibility that MTSOD1 has a pathogenic effect early in life that our later knockdown did not affect. Despite the more limited amelioration of disease than expected, the effect of the knockdown on disease supports the value of this approach in FALS patients and asymptomatic individuals with SOD1 mutations.

Metalloproteinase alterations in the bone marrow of ALS patients

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease, nowadays considered as suitable candidate for autologous stem therapy with bone marrow (BM). A careful characterization of BM stem cell (SC) compartment is mandatory before its extensive application to clinic. Indeed, widespread systemic involvement has been recently advocated given that non-neuronal neighboring cells actively influence the pathological neuronal loss. We therefore investigated BM samples from 21 ALS patients and reported normal hematopoietic biological properties while an atypical behavior and impaired SC capabilities affected only the mesenchymal compartment. Moreover, by quantitative real-time approach, we observed altered Collagen IV and Metalloproteinase-9 levels in patients' derived mesenchymal stem cells (MSCs). Widespread metalloproteinase (MMPs) and their tissue inhibitor (TIMPs) alterations were established by multiplex ELISA analysis, demonstrating diffuse enzymatic variations in MSC compartment. Since MMPs act as fundamental effectors of extra-cellular matrix remodeling and stem cell mobilization, their modifications in ALS may influence reparative mechanisms effective in counteracting the pathology. In conclusion, ALS is further confirmed to be a systemic disease, not restricted to the nervous system, but affecting also the BM stromal compartment, even in sporadic cases. Therefore, therapeutic implantation of autologous BM derived SC in ALS patients needs to be carefully reevaluated.

Moderate exercise delays the motor performance decline in a transgenic model of ALS

The relationship between exercise and amyotrophic lateral sclerosis (ALS), a neurodegenerative disorder characterized by motor neuron loss, rapidly progressive weakness and early death has been controversial. We studied the effect of a high (HEX) and moderate-level exercise (MEX) on body weight, motor performance and motor neuron counts in the ventral horn of spinal cords in a transgenic mouse model of ALS (G93A-SOD1) that overexpresses a mutated form of the human SOD1 gene that is a cause of familial ALS. These transgenic mice show several similarities to the human disease, including rapid progressive motor weakness from 100 days of age and premature death at around 135 days of age. Mice were exposed to high or mid-level exercise of left sedentary (SED). At 70, 95 and 120 days of age, spinal cords were processed following euthanasia. Motor neurons larger than 15 mum in diameter were counted with a design-based stereological protocol using an optical fractionator probe in the ventral horn of different regions of the cord and compared to wild-type littermates. Moderate exercise delayed the onset of motor deficit by over a week. High exercise slightly but significantly hastened the onset of motor performance deficits. Motor neuron density in the lumbar cord was significantly higher in MEX group compared to SED at 95 days of age. These results show the beneficial effects of moderate exercise on the preservation of motor performance that correlates with higher motor neuron density in the ventral horn of the lumbar spinal cord in G93A mice.

T cell-microglial dialogue in Parkinson's disease and amyotrophic lateral sclerosis: are we listening?

Neuroinflammation is a pathological hallmark in Parkinson's disease (PD) and amyotrophic lateral sclerosis (ALS), and is characterized by activated microglia and infiltrating T cells at sites of neuronal injury. In PD and ALS, neurons do not die alone; neuronal injury is non-cell-autonomous and depends on a well-orchestrated dialogue in which neuronally secreted misfolded proteins activate microglia and initiate a self-propagating cycle of neurotoxicity. Diverse populations and phenotypes of CD4(+) T cells crosstalk with microglia, and depending on their activation status, influence this dialogue and promote neuroprotection or neurotoxicity. A greater understanding of the T cell population that mediates these effects, as well as the molecular signals involved should provide targets for neuroprotective immunomodulation to treat these devastating neurodegenerative diseases.

Transient structural distortion of metal-free Cu/Zn superoxide dismutase triggers aberrant oligomerization

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease linked to the misfolding of Cu/Zn superoxide dismutase (SOD1). ALS-related defects in SOD1 result in a gain of toxic function that coincides with aberrant oligomerization. The structural events triggering oligomerization have remained enigmatic, however, as is the case in other protein-misfolding diseases. Here, we target the critical conformational change that defines the earliest step toward aggregation. Using nuclear spin relaxation dispersion experiments, we identified a short-lived (0.4 ms) and weakly populated (0.7%) conformation of metal-depleted SOD1 that triggers aberrant oligomerization. This excited state emanates from the folded ground state and is suppressed by metal binding, but is present in both the disulfide-oxidized and disulfide-reduced forms of the protein. Our results pinpoint a perturbed region of the excited-state structure that forms intermolecular contacts in the earliest nonnative dimer/oligomer. The conformational transition that triggers oligomerization is a common feature of WT SOD1 and ALS-associated mutants that have widely different physicochemical properties. But compared with WT SOD1, the mutants have enhanced structural distortions in their excited states, and in some cases slightly higher excited-state populations and lower kinetic barriers, implying increased susceptibility to oligomerization. Our results provide a unified picture that highlights both (i) a common denominator among different SOD1 variants that may explain why diverse mutations cause the same disease, and (ii) a structural basis that may aid in understanding how different mutations affect disease propensity and progression.

Activated protein C therapy slows ALS-like disease in mice by transcriptionally inhibiting SOD1 in motor neurons and microglia cells

Activated protein C (APC) is a signaling protease with anticoagulant activity. Here, we have used mice expressing a mutation in superoxide dismutase-1 (SOD1) that is linked to amyotrophic lateral sclerosis (ALS) to show that administration of APC or APC analogs with reduced anticoagulant activity after disease onset slows disease progression and extends survival. A proteolytically inactive form of APC with reduced anticoagulant activity provided no benefit. APC crossed the blood-spinal cord barrier in mice via endothelial protein C receptor. When administered after disease onset, APC eliminated leakage of hemoglobin-derived products across the blood-spinal cord barrier and delayed microglial activation. In microvessels, motor neurons, and microglial cells from SOD1-mutant mice and in cultured neuronal cells, APC transcriptionally downregulated SOD1. Inhibition of SOD1 synthesis in neuronal cells by APC required protease-activated receptor-1 (PAR1) and PAR3, which inhibited nuclear transport of the Sp1 transcription factor. Diminished mutant SOD1 synthesis by selective gene excision within endothelial cells did not alter disease progression, which suggests that diminished mutant SOD1 synthesis in other cells, including motor neurons and microglia, caused the APC-mediated slowing of disease. The delayed disease progression in mice after APC administration suggests that this approach may be of benefit to patients with familial, and possibly sporadic, ALS.

Latent cluster analysis of ALS phenotypes identifies prognostically differing groups

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is a degenerative disease predominantly affecting motor neurons and manifesting as several different phenotypes. Whether these phenotypes correspond to different underlying disease processes is unknown. We used latent cluster analysis to identify groupings of clinical variables in an objective and unbiased way to improve phenotyping for clinical and research purposes.

METHODS

Latent class cluster analysis was applied to a large database consisting of 1467 records of people with ALS, using discrete variables which can be readily determined at the first clinic appointment. The model was tested for clinical relevance by survival analysis of the phenotypic groupings using the Kaplan-Meier method.

RESULTS

The best model generated five distinct phenotypic classes that strongly predicted survival (p<0.0001). Eight variables were used for the latent class analysis, but a good estimate of the classification could be obtained using just two variables: site of first symptoms (bulbar or limb) and time from symptom onset to diagnosis (p<0.00001).

CONCLUSION

The five phenotypic classes identified using latent cluster analysis can predict prognosis. They could be used to stratify patients recruited into clinical trials and generating more homogeneous disease groups for genetic, proteomic and risk factor research.

Glutamate release from astrocytic gliosomes under physiological and pathological conditions

Glial subcellular particles (gliosomes) have been purified from rat cerebral cortex or mouse spinal cord and investigated for their ability to release glutamate. Confocal microscopy showed that gliosomes are enriched with glia-specific proteins, such as GFAP and S-100 but not neuronal proteins, such as PSD-95, MAP-2, and beta-tubulin III. Furthermore, gliosomes exhibit labeling neither for integrin-alphaM nor for myelin basic protein, specific for microglia and oligodendrocytes, respectively. The gliosomal fraction contains proteins of the exocytotic machinery coexisting with GFAP. Consistent with ultrastructural analysis, several nonclustered vesicles are present in the gliosome cytoplasm. Finally, gliosomes represent functional organelles that actively export glutamate when subjected to releasing stimuli, such as ionomycin, high KCl, veratrine, 4-aminopyridine, AMPA, or ATP by mechanisms involving extracellular Ca2+, Ca2+ release from intracellular stores as well as reversal of glutamate transporters. In addition, gliosomes can release glutamate also by a mechanism involving heterologous transporter activation (heterotransporters) located on glutamate-releasing and glutamate transporter-expressing (homotransporters) gliosomes. This glutamate release involves reversal of glutamate transporters and anion channel opening, but not exocytosis. Both the exocytotic and the heterotransporter-mediated glutamate release were more abundant in gliosomes prepared from the spinal cord of transgenic mice, model of amyotrophic lateral sclerosis, than in controls; suggesting the involvement of astrocytic glutamate release in the excitotoxicity proposed as a cause of motor neuron degeneration. The results support the view that gliosomes may represent a viable preparation that allows to study mechanisms of astrocytic transmitter release and its regulation in healthy animals and in animal models of brain diseases.

Lack of evidence of monomer/misfolded superoxide dismutase-1 in sporadic amyotrophic lateral sclerosis

OBJECTIVE

In familial amyotrophic lateral sclerosis (fALS) harboring superoxide dismutase (SOD1) mutations (fALS1), SOD1 toxicity has been linked to its propensity to misfold and aggregate. It has recently been proposed that misfolded SOD1 may be causative of all types of ALS, including sporadic cases (sALS). In the present study, we have used a specific antibody to test for the presence of monomer/misfolded SOD1 in sALS.

METHODS

Sections from lumbar spinal cords of 5 fALS1 cases, 13 sALS cases, and 1 non-SOD1 fALS case were labeled immunocytochemically using SOD1-exposed-dimer-interface (SEDI) antibody, which we have previously validated as being specific for pathological monomer/misfolded forms of SOD1.

RESULTS

Monomer/misfolded SOD1 was detected with SEDI antibody in all 5 of the fALS1 cases, localizing predominantly to hyaline conglomerate inclusions, a specific pathological feature of fALS1. In contrast, monomer/misfolded SOD1 was not detected in any of the 13 sALS cases or in the non-SOD1 fALS cases. These results were confirmed by immunoprecipitation.

INTERPRETATION

Although SEDI antibody does not necessarily label all misfolded forms of SOD1, these findings show a distinct difference between fALS1 and sALS, and do not support that monomer/misfolded SOD1 is a common disease entity linking all types of ALS. This is important to our understanding of ALS disease pathogenesis and to considerations of the applicability of using therapeutics that target misfolded SOD1 to non-SOD1-related cases. Ann Neurol 2009;66:75-80.

Biological and chemical approaches to diseases of proteostasis deficiency

Many diseases appear to be caused by the misregulation of protein maintenance. Such diseases of protein homeostasis, or "proteostasis," include loss-of-function diseases (cystic fibrosis) and gain-of-toxic-function diseases (Alzheimer's, Parkinson's, and Huntington's disease). Proteostasis is maintained by the proteostasis network, which comprises pathways that control protein synthesis, folding, trafficking, aggregation, disaggregation, and degradation. The decreased ability of the proteostasis network to cope with inherited misfolding-prone proteins, aging, and/or metabolic/environmental stress appears to trigger or exacerbate proteostasis diseases. Herein, we review recent evidence supporting the principle that proteostasis is influenced both by an adjustable proteostasis network capacity and protein folding energetics, which together determine the balance between folding efficiency, misfolding, protein degradation, and aggregation. We review how small molecules can enhance proteostasis by binding to and stabilizing specific proteins (pharmacologic chaperones) or by increasing the proteostasis network capacity (proteostasis regulators). We propose that such therapeutic strategies, including combination therapies, represent a new approach for treating a range of diverse human maladies.

Aggregation of copper-zinc superoxide dismutase in familial and sporadic ALS

Amyotrophic lateral sclerosis (ALS) is a progressive, fatal neurodegenerative disease characterized by the selective death of motor neurons. While the most common form of ALS is sporadic and has no known cause, a small subset of cases is familial because of underlying genetic mutations. The best-studies example of familial ALS is that caused by mutations in the protein copper-zinc superoxide dismutase. The formation of SOD1-rich inclusions in the spinal cord is an early and prominent feature of SOD1-linked familial ALS in human patients and animal models of this disease. These inclusions have been shown to consist of SOD1-rich fibrils, suggesting that the conversion of soluble SOD1 into amyloid fibrils may play an important role in the etiology of familial ALS. SOD1 is also present in inclusions found in spinal cords of sporadic ALS patients, allowing speculations to arise regarding a possible involvement of SOD1 in the sporadic form of this disease. We here review the recent research on the significance, causes, and mechanisms of SOD1 fibril formation from a biophysical perspective.

Immunological detection of N-formylkynurenine in oxidized proteins

Reactions of tryptophan residues in proteins with radical and other oxidative species frequently lead to cleavage of the indole ring, modifying tryptophan residues into N-formylkynurenine (NFK) and kynurenine. Tryptophan modification has been detected in physiologically important proteins and has been associated with a number of human disease conditions. Modified residues have been identified through various combinations of proteomic analyses, tryptic digestion, HPLC, and mass spectrometry. Here we present a novel, immunological approach using polyclonal antiserum for detection of NFK. The specificity of our antiserum is confirmed using photooxidation and radical-mediated oxidation of proteins with and without tryptophan residues. The sensitivity of our antiserum is validated through detection of NFK in photooxidized myoglobin (two tryptophan residues) and in carbonate radical-oxidized human SOD1, which contains a single tryptophan residue. Analysis of photooxidized milk also shows that our antiserum can detect NFK residues in a mixture of proteins. Results from mass spectrometric analysis of photooxidized myoglobin samples corroborate the immunological data, detecting an increase in NFK content as the extent of photooxidation increases.

Changes in the spinal cord proteome of an amyotrophic lateral sclerosis murine model determined by differential in-gel electrophoresis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder characterized by loss of motor neurons resulting in progressive paralysis. To date, more than 140 different mutations in the gene encoding CuZn-superoxide dismutase (SOD1) have been associated with ALS. Several transgenic murine models exist in which various mutant SOD1s are expressed. We used DIGE to analyze the changes in the spinal cord proteome induced by expression of the unstable SOD1 truncation mutant G127insTGGG (G127X) in mice. Unlike mutants used in most other models, G127X lacks SOD activity and is present at low levels, thus reducing the risk of overexpression artifacts. The mice were analyzed at their peak body weights just before onset of symptoms. Variable importance plot analysis showed that 420 of 1,800 detected protein spots contributed significantly to the differences between the groups. By MALDI-TOF MS analysis, 54 differentially regulated proteins were identified. One spot was found to be a covalently linked mutant SOD1 dimer, apparently analogous to SOD1-immunoreactive bands migrating at double the molecular weight of SOD1 monomers previously detected in humans and mice carrying mutant SOD1s and in sporadic ALS cases. Analyses of affected functional pathways and the subcellular representation of alterations suggest that the toxicity exerted by mutant SODs induces oxidative stress and affects mitochondria, cellular assembly/organization, and protein degradation.

Current hypotheses for the underlying biology of amyotrophic lateral sclerosis

The mechanisms involved in selective motor neuron degeneration in amyotrophic lateral sclerosis remain unknown more than 135 years after the disease was first described. Although most cases have no known cause, mutations in the gene encoding Cu/Zn superoxide dismutase (SOD1) have been implicated in a fraction of familial cases of the disease. Transgenic mouse models with mutations in the SOD1 gene and other ALS genes develop pathology reminiscent of the disorder, including progressive death of motor neurons, and have provided insight into the pathogenesis of the disease but have consistently failed to predict therapeutic efficacy in humans. However, emerging research has demonstrated that mutations and pathology associated with the TDP-43 gene and protein may be more common than SOD1 mutations in familial and sporadic ALS. Putative mechanisms of toxicity targeting motor neurons include oxidative damage, accumulation of intracellular aggregates, mitochondrial dysfunction, defects in axonal transport, growth factor deficiency, aberrant RNA metabolism, glial cell pathology, and glutamate excitotoxicity. Convergence of these pathways is likely to mediate disease onset and progression.

Wild-type SOD1 overexpression accelerates disease onset of a G85R SOD1 mouse

Approximately 10% of amyotrophic lateral sclerosis (ALS) cases are familial (FALS), and approximately 25% of FALS cases are caused by mutations in Cu/Zn superoxide dismutase type 1 (SOD1). Mutant (MT) SOD1 is thought to be pathogenic because it misfolds and aggregates. A number of transgenic mice have been generated that express different MTSOD1s as transgenes and exhibit an ALS-like disease. Although one study found that overexpression of human wild-type (WT) SOD1 did not affect disease in G85R transgenic mice, more recent reports claim that overexpression of WTSOD1 in other MTSOD1 transgenic mice hastened disease, raising a possibility that the effect of WTSOD1 overexpression in this FALS mouse model is mutant-specific. In order to clarify this issue, we studied the effect of WTSOD1 overexpression in a G85R transgenic mouse that we recently generated. We found that G85R/WTSOD1 double transgenic mice had an acceleration of disease onset and shortened survival compared with G85R single transgenic mice; in addition, there was an earlier appearance of pathological and immunohistochemical abnormalities. The spinal cord insoluble fraction from G85R/WTSOD1 mice had evidence of G85R-WTSOD1 heterodimers and WTSOD1 homodimers (in addition to G85R homodimers) with intermolecular disulfide bond cross-linking. These studies suggest that WTSOD1 can be recruited into disease-associated aggregates by redox processes, providing an explanation for the accelerated disease seen in G85R mice following WTSOD1 overexpression, and suggesting the importance of incorrect disulfide-linked protein as key to MTSOD1 toxicity.

Polymorphism of the SOD1-DNA aggregation species can be modulated by DNA

Proteinaceous aggregates rich in copper, zinc superoxide dismutase (SOD1) have been found in both in vivo and in vitro models. We have shown that double-stranded DNA that acts as a template accelerates the in vitro formation of wild-type SOD1 aggregates. Here, we examined the polymorphism of templated-SOD1 aggregates generated in vitro upon association with DNA under different conditions. Electron microscopy imaging indicates that this polymorphism is capable of being manipulated by the shapes, structures, and doses of the DNAs tested. The nanometer- and micrometer-scale aggregates formed under acidic conditions and under neutral conditions containing ascorbate fall into three classes: aggregate monomers, oligomeric aggregates, and macroaggregates. The aggregate monomers observed at given DNA doses exhibit a polymorphism that is markedly corresponded to the coiled shapes of linear DNA and structures of plasmid DNA. On the other hand, the regularly branched structures observed under both atomic force microscopy and optical microscope indicate that the DNAs tested are simultaneously condensed into a nanoparticle with a specific morphology during SOD1 aggregation, revealing that SOD1 aggregation and DNA condensation are two concurrent phenomena. The results might provide the basis of therapeutic approaches to suppress the formation of toxic protein oligomers or aggregates by screening the toxicity of the protein aggregates with various sizes and morphologies.

Pathways of methamphetamine toxicity

Methamphetamine (METH) is a drug of abuse which is neurotoxic for the nigrostriatal system. METH-induced neurodegeneration involves production of reactive oxygen species, triggering autophagic vacuoles within nigral neurons of chronic abusers of METH. In fact, Cu,Zn-superoxide dismutase 1 (SOD1) is a critical protein for the neurotoxic effects of METH on DA neurons. Moreover, mutations in the SOD1 gene cause amyotrophic lateral sclerosis, a dramatic neurodegenerative disorder. In the present paper we demonstrate that in G93A transgenic mice, overexpressing the ALS-linked mutant form of SOD1, surviving motor neurons share common intracellular alterations with METH-exposed DA neurons. We hypothesize that in mutant SOD1 transgenic mice, a defective autophagy might be responsible for the neurotoxic effects seen with in nigral neurons during METH toxicity.

TDP-43 expression in mouse models of amyotrophic lateral sclerosis and spinal muscular atrophy

Background

Redistribution of nuclear TAR DNA binding protein 43 (TDP-43) to the cytoplasm and ubiquitinated inclusions of spinal motor neurons and glial cells is characteristic of amyotrophic lateral sclerosis (ALS) pathology. Recent evidence suggests that TDP-43 pathology is common to sporadic ALS and familial ALS without SOD1 mutation, but not SOD1-related fALS cases. Furthermore, it remains unclear whether TDP-43 abnormalities occur in non-ALS forms of motor neuron disease. Here, we characterise TDP-43 localisation, expression levels and post-translational modifications in mouse models of ALS and spinal muscular atrophy (SMA).

Results

TDP-43 mislocalisation to ubiquitinated inclusions or cytoplasm was notably lacking in anterior horn cells from transgenic mutant SOD1^G93A mice. In addition, abnormally phosphorylated or truncated TDP-43 species were not detected in fractionated ALS mouse spinal cord or brain. Despite partial colocalisation of TDP-43 with SMN, depletion of SMN- and coilin-positive Cajal bodies in motor neurons of affected SMA mice did not alter nuclear TDP-43 distribution, expression or biochemistry in spinal cords.

Conclusion

These results emphasise that TDP-43 pathology characteristic of human sporadic ALS is not a core component of the neurodegenerative mechanisms caused by SOD1 mutation or SMN deficiency in mouse models of ALS and SMA, respectively.

A drosophila model for amyotrophic lateral sclerosis reveals motor neuron damage by human SOD1

Amyotrophic lateral sclerosis (ALS) is a motor neuron disease that leads to loss of motor function and early death. About 5% of cases are inherited, with the majority of identified linkages in the gene encoding copper, zinc-superoxide dismutase (SOD1). Strong evidence indicates that the SOD1 mutations confer dominant toxicity on the protein. To provide new insight into mechanisms of ALS, we have generated and characterized a model for familial ALS in Drosophila with transgenic expression of human SOD1. Expression of wild type or disease-linked (A4V, G85R) mutants of human SOD1 selectively in motor neurons induced progressive climbing deficits. These effects were accompanied by defective neural circuit electrophysiology, focal accumulation of human SOD1 protein in motor neurons, and a stress response in surrounding glia. However, toxicity was not associated with oligomerization of SOD1 and did not lead to neuronal loss. These studies uncover cell-autonomous injury by SOD1 to motor neurons in vivo, as well as non-autonomous effects on glia, and provide the foundation for new insight into injury and protection of motor neurons in ALS.

Mistranslation-induced protein misfolding as a dominant constraint on coding-sequence evolution

Strikingly consistent correlations between rates of coding-sequence evolution and gene expression levels are apparent across taxa, but the biological causes behind the selective pressures on coding-sequence evolution remain controversial. Here, we demonstrate conserved patterns of simple covariation between sequence evolution, codon usage, and mRNA level in E. coli, yeast, worm, fly, mouse, and human that suggest that all observed trends stem largely from a unified underlying selective pressure. In metazoans, these trends are strongest in tissues composed of neurons, whose structure and lifetime confer extreme sensitivity to protein misfolding. We propose, and demonstrate using a molecular-level evolutionary simulation, that selection against toxicity of misfolded proteins generated by ribosome errors suffices to create all of the observed covariation. The mechanistic model of molecular evolution that emerges yields testable biochemical predictions, calls into question the use of nonsynonymous-to-synonymous substitution ratios (Ka/Ks) to detect functional selection, and suggests how mistranslation may contribute to neurodegenerative disease.

Protein biomarkers for amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a progressive motor neuron disease with largely unknown pathogenesis that typically results in death within a few years from diagnosis. There are currently no effective therapies for ALS. Clinical diagnosis usually takes several months to complete and the long delay between symptom onset and diagnosis limits the possibilities for effective intervention and clinical trials. The establishment of protein biomarkers for ALS may aid an earlier diagnosis, facilitating the search for effective therapeutic interventions and monitoring drug efficacy during clinical trials. Biomarkers could also be used to discriminate between subtypes of ALS, to measure disease progression and to detect susceptibility for developing ALS or monitor adverse effects of drug treatment. The present review will discuss the opportunities and proteomic platforms used for biomarker discovery efforts in ALS, summarizing putative ALS protein biomarkers identified in different biofluids.

Protein kinase Cepsilon binds peripherin and induces its aggregation, which is accompanied by apoptosis of neuroblastoma cells

A hallmark of the afflicted nervous tissue in amyotrophic lateral sclerosis is the presence of protein aggregates, which to a large extent contain the intermediate filament protein peripherin. Here we show that activation of protein kinase C (PKC) or overexpression of PKCepsilon induces the aggregation of peripherin in cultured neuroblastoma cells with elevated amounts of peripherin. The formation of aggregates was coupled to an increased apoptosis, suggesting a functional link between these events. Both induction of aggregates and apoptosis were suppressed in cells that had been transfected with small interfering RNAs targeting PKCepsilon. PKCepsilon and peripherin associate as shown by co-immunoprecipitation, and the interaction is dependent on and mediated by the C1b domain of PKCepsilon. The interaction was specific for PKCepsilon since corresponding structures from other isoforms did not co-precipitate peripherin, with the exception for PKCeta and -, which pulled down minute amounts. PKCepsilon interacts with vimentin through the same structures but does not induce its aggregation. When the PKCepsilon C1b domain is expressed in neuroblastoma cells together with peripherin, both phorbol ester-induced peripherin aggregation and apoptosis are abolished, supporting a model in which PKCepsilon through its interaction with peripherin facilitates its aggregation and subsequent cell death. These events may be prevented by expressing molecules that bind peripherin at the same site as PKCepsilon.

Combining growth factor and stem cell therapy for amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease where motor neurons within the brain and spinal cord are lost, leading to paralysis and death. Certain growth factors should, in principle, be able to protect dying motor neurons. However, targeted delivery to the spinal cord or brain has been a constant problem. There is also accumulating evidence that glial cells might play a crucial role in maintaining motor neuron function and survival in ALS. Stem cells isolated and expanded in culture can be modified to release growth factors and generate glial cells following transplantation into the spinal cord or brain. As such, they might be able to both detoxify the local environment around dying motor neurons and deliver trophic factors. Here we examine the feasibility of translating these findings into new treatments for ALS patients.

Amyotrophic lateral sclerosis: from current developments in the laboratory to clinical implications

Amyotrophic lateral sclerosis (ALS) is a late-onset progressive degeneration of motor neurons occurring both as a sporadic and a familial disease. The etiology of ALS remains unknown, but one fifth of instances are due to specific gene defects, the best characterized of which is point mutations in the gene coding for Cu/Zn superoxide dismutase (SOD1). Because sporadic and familial ALS affect the same neurons with similar pathology, it is hoped that understanding these gene defects will help in devising therapies effective in both forms. A wealth of evidence has been collected in rodents made transgenic for mutant SOD1, which represent the best available models for familial ALS. Mutant SOD1 likely induces selective vulnerability of motor neurons through a combination of several mechanisms, including protein misfolding, mitochondrial dysfunction, oxidative damage, cytoskeletal abnormalities and defective axonal transport, excitotoxicity, inadequate growth factor signaling, and inflammation. Damage within motor neurons is enhanced by noxious signals originating from nonneuronal neighboring cells, where mutant SOD1 induces an inflammatory response that accelerates disease progression. The clinical implication of these findings is that promising therapeutic approaches can be derived from multidrug treatments aimed at the simultaneous interception of damage in both motor neurons and nonmotor neuronal cells.

Selective association of misfolded ALS-linked mutant SOD1 with the cytoplasmic face of mitochondria

Mutations in copper/zinc superoxide dismutase (SOD1) are causative for dominantly inherited amyotrophic lateral sclerosis (ALS). Despite high variability in biochemical properties among the disease-causing mutants, a proportion of both dismutase-active and -inactive mutants are stably bound to spinal cord mitochondria. This mitochondrial proportion floats with mitochondria rather than sedimenting to the much higher density of protein, thus eliminating coincidental cosedimentation of protein aggregates with mitochondria. Half of dismutase-active and approximately 90% of dismutase-inactive mutant SOD1 is bound to mitochondrial membranes in an alkali- and salt-resistant manner. Sensitivity to proteolysis and immunoprecipitation with an antibody specific for misfolded SOD1 demonstrate that in all mutant SOD1 models, misfolded SOD1 is deposited onto the cytoplasmic face of the outer mitochondrial membrane, increasing antigenic accessibility of the normally structured electrostatic loop. Misfolded mutant SOD1 binding is both restricted to spinal cord and selective for mitochondrial membranes, implicating exposure to mitochondria of a misfolded mutant SOD1 conformer mediated by a unique, tissue-selective composition of cytoplasmic chaperones, components unique to the cytoplasmic face of spinal mitochondria to which misfolded SOD1 binds, or misfolded SOD1 conformers unique to spinal cord that have a selective affinity for mitochondrial membranes.