An in vitro model for Lewy body-like hyaline inclusion/astrocytic hyaline inclusion: induction by ER stress with an ALS-linked SOD1 mutation

Yeast Models of Amyotrophic Lateral Sclerosis Type 8 Mimic Phenotypes Seen in Mammalian Cells Expressing Mutant VAPBP56S

Amyotrophic lateral sclerosis (ALS) is a complex neurodegenerative disease that results in the loss of motor neurons and can occur sporadically or due to genetic mutations. Among the 30 genes linked to familial ALS, a P56S mutation in VAPB, an ER-resident protein that functions at membrane contact sites, causes ALS type 8. Mammalian cells expressing VAPBP56S have distinctive phenotypes, including ER collapse, protein and/or membrane-containing inclusions, and sensitivity to ER stress. VAPB is conserved through evolution and has two homologs in budding yeast, SCS2 and SCS22. Previously, a humanized version of SCS2 bearing disease-linked mutations was described, and it caused Scs2-containing inclusions when overexpressed in yeast. Here, we describe a yeast model for ALS8 in which the two SCS genes are deleted and replaced with a single chromosomal copy of either wild-type or mutant yeast SCS2 or human VAPB expressed from the SCS2 promoter. These cells display ER collapse, the formation of inclusion-like structures, and sensitivity to tunicamycin, an ER stress-inducing drug. Based on the phenotypic similarity to mammalian cells expressing VAPBP56S, we propose that these models can be used to study the molecular basis of cell death or dysfunction in ALS8. Moreover, other conserved ALS-linked genes may create opportunities for the generation of yeast models of disease.

Functional role of WW domain-containing proteins in tumor biology and diseases: Insight into the role in ubiquitin-proteasome system

The ubiquitin-proteasome system (UPS) governs the protein degradation process and balances proteostasis and cellular homeostasis. It is a well-controlled mechanism, in which removal of the damaged or excessive proteins is essential in driving signal pathways for cell survival or death. Accumulation of damaged proteins and failure in removal may contribute to disease initiation such as in cancers and neurodegenerative diseases. In this notion, specific protein-protein interaction is essential for the recognition of targeted proteins in UPS. WW domain plays an indispensable role in the protein-protein interactions during signaling. Among the 51 WW domain-containing proteins in the human proteomics, near one-quarter of them are involved in the UPS, suggesting that WW domains are crucial modules for driving the protein-protein binding and subsequent ubiquitination and degradation. In this review, we detail a broad spectrum of WW domains in protein-protein recognition, signal transduction, and relevance to diseases. New perspectives in dissecting the molecular interactions are provided.

Drug screening for Pelizaeus-Merzbacher disease by quantifying the total levels and membrane localization of PLP1

Background

Pelizaeus-Merzbacher disease (PMD) is caused by point mutations or copy number changes in the proteolipid protein 1 gene (PLP1). PLP1 is exclusively localized in the myelin sheath of oligodendrocytes. Amino acid-substituted PLP1 protein is unable to fold properly and is subsequently degraded and/or restrictedly translated, resulting in a decrease in the PLP1 protein level and a failure to localize to the membrane. Furthermore, misfolded proteins increase the burden on the intracellular quality control system and trafficking, finally resulting in cell apoptosis. The objective of this study was to identify therapeutic chemicals for PMD by quantifying the total levels and membrane localization of PLP1.

Method

We established a cell line stably expressing PLP1^A243V fused with green fluorescent protein in oligodendrocyte-derived MO3.13 cells. We screened a chemical library composed of drugs approved for central nervous system disorders that increased both the total intensity of PLP1^A243V in the whole cell and the cell membrane localization. We analyzed the change in the endoplasmic reticulum (ER) stress and the gene expression of candidate chemicals using a micro-array analysis. Finally, we tested the in vivo effectiveness using myelin synthesis deficient (msd) mice with Plp^A243V.

Results and conclusion

Piracetam significantly increased the PLP1^A243V intensity and membrane localization and decreased the ER stress. It was also shown to reverse the gene expression changes induced by PLP1^A243V in a micro-array analysis. However, in vivo treatment of piracetam did not improve the survival of msd mice (Plp1^A243V).

Tryptophan 32 mediates SOD1 toxicity in a in vivo motor neuron model of ALS and is a promising target for small molecule therapeutics

SOD1 misfolding, toxic gain of function, and spread are proposed as a pathological basis of amyotrophic lateral sclerosis (ALS), but the nature of SOD1 toxicity has been difficult to elucidate. Uniquely in SOD1 proteins from humans and other primates, and rarely in other species, a tryptophan residue at position 32 (W32) is predicted to be solvent exposed and to participate in SOD1 misfolding. We hypothesized that W32 is influential in SOD1 acquiring toxicity, as it is known to be important in template-directed misfolding. We tested if W32 contributes to SOD1 cytotoxicity and if it is an appropriate drug target to ameliorate ALS-like neuromuscular deficits in a zebrafish model of motor neuron axon morphology and function (swimming). Embryos injected with human SOD1 variant with W32 substituted for a serine (SOD1^W32S) had reduced motor neuron axonopathy and motor deficits compared to those injected with wildtype or disease-associated SOD1. A library of FDA-approved small molecules was ranked with virtual screening based on predicted binding to W32, and subsequently filtered for analogues using a pharmacophore model based on molecular features of the uracil moiety of a small molecule previously predicted to interact with W32 (5'-fluorouridine or 5'-FUrd). Along with testing 5'-FUrd and uridine, a lead candidate from this list was selected based on its lower toxicity and improved blood brain barrier penetrance; telbivudine significantly rescued SOD1 toxicity in a dose-dependent manner. The mechanisms whereby the small molecules ameliorated motor neuron phenotypes were specifically mediated through human SOD1 and its residue W32, because these therapeutics had no measurable impact on the effects of UBQLN4^D90A, EtOH, or tryptophan-deficient human SOD1^W32S. By substituting W32 for a more evolutionarily conserved residue (serine), we confirmed the significant influence of W32 on human SOD1 toxicity to motor neuron morphology and function; further, we performed pharmaceutical targeting of the W32 residue for rescuing SOD1 toxicity. This unique residue offers future novel insights into SOD1 stability and toxic gain of function, and therefore poses an potential target for drug therapy.

Single copy/knock-in models of ALS SOD1 in C. elegans suggest loss and gain of function have different contributions to cholinergic and glutamatergic neurodegeneration

Mutations in Cu/Zn superoxide dismutase 1 (SOD1) lead to Amyotrophic Lateral Sclerosis (ALS), a neurodegenerative disease that disproportionately affects glutamatergic and cholinergic motor neurons. Previous work with SOD1 overexpression models supports a role for SOD1 toxic gain of function in ALS pathogenesis. However, the impact of SOD1 loss of function in ALS cannot be directly examined in overexpression models. In addition, overexpression may obscure the contribution of SOD1 loss of function in the degeneration of different neuronal populations. Here, we report the first single-copy, ALS knock-in models in C. elegans generated by transposon- or CRISPR/Cas9- mediated genome editing of the endogenous sod-1 gene. Introduction of ALS patient amino acid changes A4V, H71Y, L84V, G85R or G93A into the C. elegans sod-1 gene yielded single-copy/knock-in ALS SOD1 models. These differ from previously reported overexpression models in multiple assays. In single-copy/knock-in models, we observed differential impact of sod-1 ALS alleles on glutamatergic and cholinergic neurodegeneration. A4V, H71Y, G85R, and G93A animals showed increased SOD1 protein accumulation and oxidative stress induced degeneration, consistent with a toxic gain of function in cholinergic motor neurons. By contrast, H71Y, L84V, and G85R lead to glutamatergic neuron degeneration due to sod-1 loss of function after oxidative stress. However, dopaminergic and serotonergic neuronal populations were spared in single-copy ALS models, suggesting a neuronal-subtype specificity previously not reported in invertebrate ALS SOD1 models. Combined, these results suggest that knock-in models may reproduce the neurotransmitter-type specificity of ALS and that both SOD1 loss and gain of toxic function differentially contribute to ALS pathogenesis in different neuronal populations.

In all SOD1 ALS patients, cholinergic spinal motor neurons degenerate, but degeneration of cortical glutamatergic neurons is less common. Despite decades of work, it remains unclear why some disease alleles (e.g. A4V) primarily affect cholinergic spinal neurons, while other alleles affect both cholinergic and glutamatergic neurons. New genome editing techniques allowed us to create the first C. elegans knock-in/single-copy models for SOD1 ALS by directly editing the C. elegans sod-1 gene to recreate SOD1 amino acid changes that cause ALS in patients. These new models are complementary to previously described overexpression models, which revealed mutant SOD1 toxic gain of function properties. By contrast, in the new C. elegans knock-in models, we find that both loss and gain of sod-1 function contribute to neurodegeneration. C. elegans cholinergic motor neuron loss is primarily driven by toxic gain of function, but glutamatergic neuron loss is primarily driven by loss of function. Only cholinergic and glutamatergic neurons degenerate in C. elegans knock-in models; dopaminergic, serotoninergic and GABAergic neurons do not. This pattern of neuronal loss is reminiscent of the pattern of neuronal loss seen in SOD1 ALS patients. Strikingly, in the C. elegans A4V model, only cholinergic neurons are lost. Our results suggest that an underlying premise of the ALS field–that identical pathological mechanisms lead to degeneration of cholinergic and glutamatergic neurons–should be reconsidered. Mechanisms that predominantly drive glutamatergic and cholinergic neuron degeneration in ALS may not be identical.

Clinical and neuropathological features of ALS/FTD with TIA1 mutations

Mutations in the stress granule protein T-cell restricted intracellular antigen 1 (TIA1) were recently shown to cause amyotrophic lateral sclerosis (ALS) with or without frontotemporal dementia (FTD). Here, we provide detailed clinical and neuropathological descriptions of nine cases with TIA1 mutations, together with comparisons to sporadic ALS (sALS) and ALS due to repeat expansions in C9orf72 (C9orf72+). All nine patients with confirmed mutations in TIA1 were female. The clinical phenotype was heterogeneous with a range in the age at onset from late twenties to the eighth decade (mean = 60 years) and disease duration from one to 6 years (mean = 3 years). Initial presentation was either focal weakness or language impairment. All affected individuals received a final diagnosis of ALS with or without FTD. No psychosis or parkinsonism was described. Neuropathological examination on five patients found typical features of ALS and frontotemporal lobar degeneration (FTLD-TDP, type B) with anatomically widespread TDP-43 proteinopathy. In contrast to C9orf72+ cases, caudate atrophy and hippocampal sclerosis were not prominent. Detailed evaluation of the pyramidal motor system found a similar degree of neurodegeneration and TDP-43 pathology as in sALS and C9orf72+ cases; however, cases with TIA1 mutations had increased numbers of lower motor neurons containing round eosinophilic and Lewy body-like inclusions on HE stain and round compact cytoplasmic inclusions with TDP-43 immunohistochemistry. Immunohistochemistry and immunofluorescence failed to demonstrate any labeling of inclusions with antibodies against TIA1. In summary, our TIA1 mutation carriers developed ALS with or without FTD, with a wide range in age at onset, but without other neurological or psychiatric features. The neuropathology was characterized by widespread TDP-43 pathology, but a more restricted pattern of neurodegeneration than C9orf72+ cases. Increased numbers of round eosinophilic and Lewy-body like inclusions in lower motor neurons may be a distinctive feature of ALS caused by TIA1 mutations.

Cu/Zn Superoxide Dismutase Forms Amyloid Fibrils under Near-Physiological Quiescent Conditions: The Roles of Disulfide Bonds and Effects of Denaturant

Cu/Zn superoxide dismutase (SOD1) forms intracellular aggregates that are pathological indicators of amyotrophic lateral sclerosis. A large body of research indicates that the entry point to aggregate formation is a monomeric, metal-ion free (apo), and disulfide-reduced species. Fibril formation by SOD1 in vitro has typically been reported only for harsh solvent conditions or mechanical agitation. Here we show that monomeric apo-SOD1 in the disulfide-reduced state forms fibrillar aggregates under near-physiological quiescent conditions. Monomeric apo-SOD1 with an intact intramolecular disulfide bond is highly resistant to aggregation under the same conditions. A cysteine-free variant of SOD1 exhibits fibrillization behavior and fibril morphology identical to those of disulfide-reduced SOD1, firmly establishing that intermolecular disulfide bonds or intramolecular disulfide shuffling are not required for aggregation and fibril formation. The decreased lag time for fibril formation resulting from reduction of the intramolecular disulfide bond thus primarily reflects the decreased stability of the folded state relative to partially unfolded states, rather than an active role of free sulfhydryl groups in mediating aggregation. Addition of urea to increase the amount of fully unfolded SOD1 increases the lag time for fibril formation, indicating that the population of this species does not dominate over other factors in determining the onset of aggregation. Our results contrast with previous results obtained for agitated samples, in which case amyloid formation was accelerated by denaturant. We reconcile these observations by suggesting that denaturants destabilize monomeric and aggregated species to different extents and thus affect nucleation and growth.

DBZ, a CNS-specific DISC1 binding protein, positively regulates oligodendrocyte differentiation

Recent studies have shown changes in myelin genes and alterations in white matter structure in a wide range of psychiatric disorders. Here we report that DBZ, a central nervous system (CNS)-specific member of the DISC1 interactome, positively regulates the oligodendrocyte (OL) differentiation in vivo and in vitro. In mouse corpus callosum (CC), DBZ mRNA is expressed in OL lineage cells and expression of DBZ protein peaked before MBP expression. In the CC of DBZ-KO mice, we observed delayed myelination during the early postnatal period. Although the myelination delay was mostly recovered by adulthood, OLs with immature structural features were more abundant in adult DBZ-KO mice than in control mice. DBZ was also transiently upregulated during rat OL differentiation in vitro before myelin marker expression. DBZ knockdown by RNA interference resulted in a decreased expression of myelin-related markers and a low number of cells with mature characteristics, but with no effect on the proliferation of oligodendrocyte precursor cells. We also show that the expression levels of transcription factors having a negative-regulatory role in OL differentiation were upregulated when endogenous DBZ was knocked down. These results strongly indicate that OL differentiation in rodents is regulated by DBZ.

The endoplasmic reticulum-resident chaperone heat shock protein 47 protects the Golgi apparatus from the effects of O-glycosylation inhibition

The Golgi apparatus is important for the transport of secretory cargo. Glycosylation is a major post-translational event. Recognition of O-glycans on proteins is necessary for glycoprotein trafficking. In this study, specific inhibition of O-glycosylation (Golgi stress) induced the expression of endoplasmic reticulum (ER)-resident heat shock protein (HSP) 47 in NIH3T3 cells, although cell death was not induced by Golgi stress alone. When HSP47 expression was downregulated by siRNA, inhibition of O-glycosylation caused cell death. Three days after the induction of Golgi stress, the Golgi apparatus was disassembled, many vacuoles appeared near the Golgi apparatus and extended into the cytoplasm, the nuclei had split, and cell death assay-positive cells appeared. Six hours after the induction of Golgi stress, HSP47-knockdown cells exhibited increased cleavage of Golgi-resident caspase-2. Furthermore, activation of mitochondrial caspase-9 and ER-resident unfolded protein response (UPR)-related molecules and efflux of cytochrome c from the mitochondria to the cytoplasm was observed in HSP47-knockdown cells 24 h after the induction of Golgi stress. These findings indicate that (i) the ER-resident chaperon HSP47 protected cells from Golgi stress, and (ii) Golgi stress-induced cell death caused by the inhibition of HSP47 expression resulted from caspase-2 activation in the Golgi apparatus, extending to the ER and mitochondria.

Definition of genetic events directing the development of distinct types of brain tumors from postnatal neural stem/progenitor cells

Although brain tumors are classified and treated based upon their histology, the molecular factors involved in the development of various tumor types remain unknown. In this study, we show that the type and order of genetic events directs the development of gliomas, central nervous system primitive neuroectodermal tumors, and atypical teratoid/rhabdoid-like tumors from postnatal mouse neural stem/progenitor cells (NSC/NPC). We found that the overexpression of specific genes led to the development of these three different brain tumors from NSC/NPCs, and manipulation of the order of genetic events was able to convert one established tumor type into another. In addition, loss of the nuclear chromatin-remodeling factor SMARCB1 in rhabdoid tumors led to increased phosphorylation of eIF2α, a central cytoplasmic unfolded protein response (UPR) component, suggesting a role for the UPR in these tumors. Consistent with this, application of the proteasome inhibitor bortezomib led to an increase in apoptosis of human cells with reduced SMARCB1 levels. Taken together, our findings indicate that the order of genetic events determines the phenotypes of brain tumors derived from a common precursor cell pool, and suggest that the UPR may represent a therapeutic target in atypical teratoid/rhabdoid tumors.

Mutant FUS induces endoplasmic reticulum stress in amyotrophic lateral sclerosis and interacts with protein disulfide-isomerase

Mutations in the gene encoding fused in sarcoma (FUS) are linked to amyotrophic lateral sclerosis (ALS), but the mechanisms by which these mutants trigger neurodegeneration remain unknown. Endoplasmic reticulum (ER) stress is increasingly recognized as an important and early pathway to motor neuron death in ALS. FUS is normally located in the nucleus but in ALS, FUS redistributes to the cytoplasm and forms inclusions. In this study, we investigated whether FUS induces ER stress in a motor neuron like cell line (NSC-34). We demonstrate that ER stress is triggered in cells expressing mutant FUS, and this is closely associated with redistribution of mutant FUS to the cytoplasm. Mutant FUS also colocalized with protein disulfide-isomerase (PDI), an important ER chaperone, in NSC-34 cells and PDI was colocalized with FUS inclusions in human ALS lumbar spinal cords, in both sporadic ALS and mutant FUS-linked familial ALS tissues. These findings implicate ER stress in the pathophysiology of FUS, and provide evidence for common pathogenic pathways in ALS linked to the ER.

Molecular pathways of motor neuron injury in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a genetically diverse disease. At least 15 ALS-associated gene loci have so far been identified, and the causative gene is known in approximately 30% of familial ALS cases. Less is known about the factors underlying the sporadic form of the disease. The molecular mechanisms of motor neuron degeneration are best understood in the subtype of disease caused by mutations in superoxide dismutase 1, with a current consensus that motor neuron injury is caused by a complex interplay between multiple pathogenic processes. A key recent finding is that mutated TAR DNA-binding protein 43 is a major constituent of the ubiquitinated protein inclusions in ALS, providing a possible link between the genetic mutation and the cellular pathology. New insights have also indicated the importance of dysregulated glial cell-motor neuron crosstalk, and have highlighted the vulnerability of the distal axonal compartment early in the disease course. In addition, recent studies have suggested that disordered RNA processing is likely to represent a major contributing factor to motor neuron disease. Ongoing research on the cellular pathways highlighted in this Review is predicted to open the door to new therapeutic interventions to slow disease progression in ALS.

Protein disulfide isomerase-immunopositive inclusions in patients with amyotrophic lateral sclerosis

The major pathological hallmarks of amyotrophic lateral sclerosis (ALS) are neuronal cytoplasmic inclusions (NCIs) and swollen neurites. Superoxide dismutase (SOD)-1-immunopositive NCIs are observed in patients with familial ALS (FALS), and TAR DNA-binding protein 43kDa (TDP-43)-immunopositive NCIs are found in patients with sporadic ALS (SALS). Protein disulfide isomerase (PDI) is a member of the thioredoxin superfamily and is believed to accelerate the folding of disulfide-bonded proteins by catalyzing the disulfide interchange reaction, which is the rate-limiting step during protein folding in the luminal space of the endoplasmic reticulum. Post mortem spinal cord specimens from five patients with SALS and one with FALS (I113T), and five normal controls were utilized in this immunohistochemical study. We found PDI-immunopositive swollen neurites and NCIs in the patients with ALS. Furthermore, PDI was colocalized with TDP-43 and SOD1 in NCIs. The accumulation of misfolding proteins may disturb axon transport and make swollen neurites. As the motor neuron is the longest cell in the nervous system, the motor system may selectively be disturbed. In conclusion, we assume that PDI is S-nitrosylated in the affected neurons, which inhibits its enzymatic activity and thus allows protein misfolding to occur in ALS.

Amyotrophic lateral sclerosis pathogenesis: a journey through the secretory pathway

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

Ultrastructural diversity of inclusions and aggregations in the lumbar spinal cord of SOD1-G93A transgenic mice

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by selective motor neuron death. We report the characteristics of ultrastructural pathological changes of inclusions and aggregations in the neuronal axons, glial cells and ventral roots of lumbar spinal cord in SOD1-G93A transgenic mice using light and electron transmission microscope at different stages of disease. The most noteworthy is that mutant SOD1 accumulations in the cytoplasm of motor neurons precede the numerous inclusions. Inclusions manifested differently according to the specified locations. This study provided further information to the previous reports about pathological changes of ALS.

HtrA2/Omi-immunoreactive intraneuronal inclusions in the anterior horn of patients with sporadic and Cu/Zn superoxide dismutase (SOD1) mutant amyotrophic lateral sclerosis

AIMS

HtrA2/Omi is a mitochondrial serine protease that promotes the apoptotic processes, but the relationship between HtrA2/Omi and amyotrophic lateral sclerosis (ALS) is still unknown. The purpose of the present study was to determine whether abnormal expression of HtrA2/Omi occurs in patients with ALS.

METHODS

We prepared autopsied spinal cord tissues from 7 control subjects, 11 patients with sporadic ALS (SALS) and 4 patients with Cu/Zn superoxide dismutase (SOD1)-related familial ALS (FALS). We then performed immunohistochemical studies on HtrA2/Omi using formalin-fixed, paraffin-embedded sections from all of the cases.

RESULTS

In the control subjects, the anterior horn cells were mildly to moderately immunostained with HtrA2/Omi. In the patients with SALS, strong HtrA2/Omi immunoreactivity was found in some skein-like inclusions and round hyaline inclusions as well as many spheroids, but Bunina bodies were immunonegative for HtrA2/Omi. In the patients with SOD1-related FALS, Lewy body-like hyaline inclusions were observed in three cases and conglomerate inclusions were observed in the remaining case, and both types of inclusions were intensely immunopositive for HtrA2/Omi.

CONCLUSIONS

These results suggest that abnormal accumulations of HtrA2/Omi may occur in several types of motor neuronal inclusions in the anterior horn from SALS and SOD1-linked FALS cases, and that HtrA2/Omi may be associated with the pathogenesis of both types of ALS.

Caspase-4 is partially cleaved by calpain via the impairment of Ca2+ homeostasis under the ER stress

In the previous reports, we showed that caspase-4, which has high homology to caspase-12, plays an important role in the neural cell death via the endoplasmic reticulum (ER) stress. In addition, we elucidated the involvement of the familial Alzheimer's disease (AD)-linked presenilin-1 (PS1) mutation and beta-amyloid induced-apoptotic signaling in human neural cells in the activation (cleavage) of caspase-4. These results suggest the involvement of caspase-4 in the cell death observed in AD. To elucidate the mechanism of the cleavage of caspase-4 under ER stress, we used EGTA, a Ca(2+) chelator, because the cleavage caspase-12 has reported to be regulated by the calpain. As the results, EGTA inhibited the cleavage of caspase-4 in a concentration-dependent manner. In addition, inhibitors of calpain, which are activated by the Ca(2+), also inhibited the cleavage of caspase-4. Furthermore, EGTA and caplain inhibitors rescued the neural cell death under the ER stress. These results suggest that the disturbance of Ca(2+) homeostasis induced by ER stress should cause the activation of caspase-4 resulting in the neural cell death.

Protein disulphide isomerase protects against protein aggregation and is S-nitrosylated in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis is a rapidly progressing fatal neurodegenerative disease characterized by the presence of protein inclusions within affected motor neurons. Endoplasmic reticulum stress leading to apoptosis was recently recognized to be an important process in the pathogenesis of sporadic human amyotrophic lateral sclerosis as well as in transgenic models of mutant superoxide dismutase 1-linked familial amyotrophic lateral sclerosis. Endoplasmic reticulum stress occurs early in disease, indicating a critical role in pathogenesis, and involves upregulation of an important endoplasmic reticulum chaperone, protein disulphide isomerase. We aimed to investigate the involvement of protein disulphide isomerase in endoplasmic reticulum stress induction, protein aggregation, inclusion formation and toxicity in amyotrophic lateral sclerosis. Motor neuron-like NSC-34 cell lines were transfected with superoxide dismutase 1 and protein disulphide isomerase encoding vectors and small interfering RNA, and examined by immunocytochemistry and immunoblotting. Expression of mutant superoxide dismutase 1 induced endoplasmic reticulum stress, predominantly in cells bearing mutant superoxide dismutase 1 inclusions but also in a proportion of cells expressing mutant superoxide dismutase 1 without visible inclusions. Over-expression of protein disulphide isomerase decreased mutant superoxide dismutase 1 aggregation, inclusion formation, endoplasmic reticulum stress induction and toxicity, whereas small interfering RNA targeting protein disulphide isomerase increased mutant superoxide dismutase 1 inclusion formation, indicating a protective role for protein disulphide isomerase against superoxide dismutase 1 misfolding. Aberrant modification of protein disulphide isomerase by S-nitrosylation of active site cysteine residues has previously been shown as an important process in neurodegeneration in Parkinson's and Alzheimer's disease brain tissue, but has not been described in amyotrophic lateral sclerosis. Using a biotin switch assay, we detected increased levels of S-nitrosylated protein disulphide isomerase in transgenic mutant superoxide dismutase 1 mouse and human sporadic amyotrophic lateral sclerosis spinal cord tissues. Hence, despite upregulation, protein disulphide isomerase is also functionally inactivated in amyotrophic lateral sclerosis, which may prevent its normal protective function and contribute to disease. We also found that a small molecule mimic of the protein disulphide isomerase active site, (+/-)-trans-1,2-bis(mercaptoacetamido)cyclohexane, protected against mutant superoxide dismutase 1 inclusion formation. These studies reveal that endoplasmic reticulum stress is important in the formation of mutant superoxide dismutase 1 inclusions, and protein disulphide isomerase has an important function in ameliorating mutant superoxide dismutase 1 aggregation and toxicity. Functional inhibition of protein disulphide isomerase by S-nitrosylation may contribute to pathophysiology in both mutant superoxide dismutase 1-linked disease and sporadic amyotrophic lateral sclerosis. Protein disulphide isomerase is therefore a novel potential therapeutic target in amyotrophic lateral sclerosis and (+/-)-trans-1,2-bis(mercaptoacetamido)cyclohexane and other molecular mimics of protein disulphide isomerase could be of benefit in amyotrophic lateral sclerosis and other neurodegenerative diseases related to protein misfolding.

A role for motoneuron subtype-selective ER stress in disease manifestations of FALS mice

The mechanisms underlying disease manifestations in neurodegeneration remain unclear, but their understanding is critical to devising effective therapies. We carry out a longitudinal analysis in vivo of identified motoneurons selectively vulnerable (VUL) or resistant (RES) to motoneuron disease (amyotrophic lateral sclerosis, ALS) and show that subtype-selective endoplasmic reticulum (ER) stress responses influence disease manifestations. VUL motoneurons were selectively prone to ER stress and showed gradually upregulated ER stress markers from birth on in three mouse models of familial ALS (FALS). 25-30 days before the earliest denervations, ubiquitin signals increased in both VUL and RES motoneurons, but an unfolded protein response coupled with microglial activation was initiated selectively in VUL motoneurons. This transition was followed by selective axonal degeneration and spreading stress. The ER stress-protective agent salubrinal attenuated disease manifestations and delayed progression, whereas chronic enhancement of ER stress promoted disease. Thus, whereas all motoneurons are preferentially affected in ALS, ER stress responses in specific motoneuron subtypes influence the progressive manifestations of weakening and paralysis.

Loss of metal ions, disulfide reduction and mutations related to familial ALS promote formation of amyloid-like aggregates from superoxide dismutase

Mutations in the gene encoding Cu-Zn superoxide dismutase (SOD1) are one of the causes of familial amyotrophic lateral sclerosis (FALS). Fibrillar inclusions containing SOD1 and SOD1 inclusions that bind the amyloid-specific dye thioflavin S have been found in neurons of transgenic mice expressing mutant SOD1. Therefore, the formation of amyloid fibrils from human SOD1 was investigated. When agitated at acidic pH in the presence of low concentrations of guanidine or acetonitrile, metalated SOD1 formed fibrillar material which bound both thioflavin T and Congo red and had circular dichroism and infrared spectra characteristic of amyloid. While metalated SOD1 did not form amyloid-like aggregates at neutral pH, either removing metals from SOD1 with its intramolecular disulfide bond intact or reducing the intramolecular disulfide bond of metalated SOD1 was sufficient to promote formation of these aggregates. SOD1 formed amyloid-like aggregates both with and without intermolecular disulfide bonds, depending on the incubation conditions, and a mutant SOD1 lacking free sulfhydryl groups (AS-SOD1) formed amyloid-like aggregates at neutral pH under reducing conditions. ALS mutations enhanced the ability of disulfide-reduced SOD1 to form amyloid-like aggregates, and apo-AS-SOD1 formed amyloid-like aggregates at pH 7 only when an ALS mutation was also present. These results indicate that some mutations related to ALS promote formation of amyloid-like aggregates by facilitating the loss of metals and/or by making the intramolecular disulfide bond more susceptible to reduction, thus allowing the conversion of SOD1 to a form that aggregates to form resembling amyloid. Furthermore, the occurrence of amyloid-like aggregates per se does not depend on forming intermolecular disulfide bonds, and multiple forms of such aggregates can be produced from SOD1.

Amyotrophic lateral sclerosis models and human neuropathology: similarities and differences

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease that primarily involves the motor neuron system. The author initially summarizes the principal features of human ALS neuropathology, and subsequently describes in detail ALS animal models mainly from the viewpoint of pathological similarities and differences. ALS animal models in this review include strains of rodents that are transgenic for superoxide dismutase 1 (SOD1), ALS2 knockout mice, and mice that are transgenic for cytoskeletal abnormalities. Although the neuropathological results obtained from human ALS autopsy cases are valuable and important, almost all of such cases represent only the terminal stage. This makes it difficult to clarify how and why ALS motor neurons are impaired at each clinical stage from disease onset to death, and as a consequence, human autopsy cases alone yield little insight into potential therapies for ALS. Although ALS animal models cannot replicate human ALS, in order to compensate for the shortcomings of studies using human ALS autopsy samples, researchers must inevitably rely on ALS animal models that can yield very important information for clarifying the pathogenesis of ALS in humans and for the establishment of reliable therapy. Of course, human ALS and all ALS animal models share one most important similarity in that both exhibit motor neuron degeneration/death. This important point of similarity has shed much light on the pathomechanisms of the motor neuron degeneration/death at the cellular and molecular levels that would not have been appreciated if only human ALS autopsy samples had been available. On the basis of the aspects covered in this review, it can be concluded that ALS animal models can yield very important information for clarifying the pathogenesis of ALS in humans and for the establishment of reliable therapy only in combination with detailed neuropathological data obtained from human ALS autopsy cases.