Microtubule-associated tau protein positive neuronal and glial inclusions in ALS

Amyloid-beta and tau protein beyond Alzheimer's disease

ABSTRACT

The aggregation of amyloid-beta peptide and tau protein dysregulation are implicated to play key roles in Alzheimer's disease pathogenesis and are considered the main pathological hallmarks of this devastating disease. Physiologically, these two proteins are produced and expressed within the normal human body. However, under pathological conditions, abnormal expression, post-translational modifications, conformational changes, and truncation can make these proteins prone to aggregation, triggering specific disease-related cascades. Recent studies have indicated associations between aberrant behavior of amyloid-beta and tau proteins and various neurological diseases, such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis, as well as retinal neurodegenerative diseases like Glaucoma and age-related macular degeneration. Additionally, these proteins have been linked to cardiovascular disease, cancer, traumatic brain injury, and diabetes, which are all leading causes of morbidity and mortality. In this comprehensive review, we provide an overview of the connections between amyloid-beta and tau proteins and a spectrum of disorders.

Upregulation of LRRK2 following traumatic brain injury does not directly phosphorylate Thr175 tau

Phosphorylated microtubule-associated protein tau (tau) aggregates are a pathological hallmark of various neurodegenerative diseases, including chronic traumatic encephalopathy and amyotrophic lateral sclerosis with cognitive impairment. While there are many residues phosphorylated on tau, phosphorylation of threonine 175 (pThr175 tau) has been shown to initiate fibril formation in vitro and is present in pathological tau aggregates in vivo. Given this, preventing Thr175 tau phosphorylation presents a potential approach to reduce fibril formation; however, the kinase(s) acting on Thr175 are not yet fully defined. Using a single controlled cortical impact rodent model of traumatic brain injury (TBI), which rapidly induces Thr175 tau phosphorylation, we observed an upregulation and alteration in subcellular localization of leucine-rich repeat kinase 2 (LRRK2), a kinase that has been implicated in tau phosphorylation. LRRK2 upregulation was evident by one-day post-injury and persisted to day 10. The most notable changes were observed in microglia at the site of injury in the cortex. To determine if the appearance of pThr175 tau was causally related to the upregulation of LRRK2 expression, we examined the ability of LRRK2 to phosphorylate Thr175in vitro by co-transfecting 2N4R human WT-tau with either LRRK2-WT, constitutively-active LRRK2-G2019S or inactive LRRK2-3XKD. We found no significant difference in the level of pThr175 tau between the overexpression of LRRK2-WT, -G2019S or -3XKD, suggesting LRRK2 does not phosphorylate tau at Thr175. Further, downstream events known to follow Thr175 phosphorylation and known to be associated with pathological tau fibril formation (pSer9-GSK3β and pThr231 tau induction) also remained unchanged. We conclude that while LRRK2 expression is altered in TBI, it does not contribute directly to pThr175 tau generation.

Progress in biophysics and molecular biology proteostasis impairment and ALS

Amyotrophic lateral sclerosis (ALS) is a rapidly progressive and fatal neurodegenerative disease that results from the loss of both upper and lower motor neurons. It is the most common motor neuron disease and currently has no effective treatment. There is mounting evidence to suggest that disturbances in proteostasis play a significant role in ALS pathogenesis. Proteostasis is the maintenance of the proteome at the right level, conformation and location to allow a cell to perform its intended function. In this review, we present a thorough synthesis of the literature that provides evidence that genetic mutations associated with ALS cause imbalance to a proteome that is vulnerable to such pressure due to its metastable nature. We propose that the mechanism underlying motor neuron death caused by defects in mRNA metabolism and protein degradation pathways converges on proteostasis dysfunction. We propose that the proteostasis network may provide an effective target for therapeutic development in ALS.

Pathogenic Effect of TP73 Gene Variants in People With Amyotrophic Lateral Sclerosis

OBJECTIVE

To identify novel disease associated loci for amyotrophic lateral sclerosis (ALS), we used sequencing data and performed in vitro and in vivo experiments to demonstrate pathogenicity of mutations identified in TP73.

METHODS

We analyzed exome sequences of 87 patients with sporadic ALS and 324 controls, with confirmatory sequencing in independent ALS cohorts of >2,800 patients. For the top hit, TP73, a regulator of apoptosis and differentiation and a binding partner and homolog of the tumor suppressor gene TP53, we assayed mutation effects using in vitro and in vivo experiments. C2C12 myoblast differentiation assays, characterization of myotube appearance, and immunoprecipitation of p53-p73 complexes were performed in vitro. In vivo, we used clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 targeting of zebrafish tp73 to assay motor neuron number and axon morphology.

RESULTS

Four heterozygous rare, nonsynonymous mutations in TP73 were identified in our sporadic ALS cohort. In independent ALS cohorts, we identified an additional 19 rare, deleterious variants in TP73. Patient TP73 mutations caused abnormal differentiation and increased apoptosis in the myoblast differentiation assay, with abnormal myotube appearance. Immunoprecipitation of mutant ΔN-p73 demonstrated that patient mutations hinder the ability of ΔN-p73 to bind p53. CRISPR/Cas9 knockout of tp73 in zebrafish led to impaired motor neuron development and abnormal axonal morphology, concordant with ALS pathology.

CONCLUSION

Together, these results strongly suggest that variants in TP73 correlate with risk for ALS and indicate a role for apoptosis in ALS disease pathology.

Alterations in Tau Metabolism in ALS and ALS-FTSD

There is increasing acceptance that amyotrophic lateral sclerosis (ALS), classically considered a neurodegenerative disease affecting almost exclusively motor neurons, is syndromic with both clinical and biological heterogeneity. This is most evident in its association with a broad range of neuropsychological, behavioral, speech and language deficits [collectively termed ALS frontotemporal spectrum disorder (ALS-FTSD)]. Although the most consistent pathology of ALS and ALS-FTSD is a disturbance in TAR DNA binding protein 43 kDa (TDP-43) metabolism, alterations in microtubule-associated tau protein (tau) metabolism can also be observed in ALS-FTSD, most prominently as pathological phosphorylation at Thr¹⁷⁵ (pThr¹⁷⁵tau). pThr¹⁷⁵ has been shown to promote exposure of the phosphatase activating domain (PAD) in the tau N-terminus with the consequent activation of GSK3β mediated phosphorylation at Thr²³¹ (pThr²³¹tau) leading to pathological oligomer formation. This pathological cascade of tau phosphorylation has been observed in chronic traumatic encephalopathy with ALS (CTE-ALS) and in both in vivo and in vitro experimental paradigms, suggesting that it is of critical relevance to the pathobiology of ALS-FTSD. It is also evident that the co-existence of alterations in the metabolism of TDP-43 and tau acts synergistically in a rodent model to exacerbate the pathology of either.

ALS-associated TBK1 variant p.G175S is defective in phosphorylation of p62 and impacts TBK1-mediated signalling and TDP-43 autophagic degradation

Mutations affecting SQSTM1 coding for p62 and TANK-Binding Kinase 1 (TBK1) have been implicated in amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD). TBK1 is a serine-threonine kinase that regulates p62's activity as an autophagy receptor via phosphorylation and also has roles in neuroinflammatory signalling pathways. The mechanisms underlying ALS and FTLD pathogenesis as a result of TBK1 mutations are incompletely understood, however, loss of TBK1 function can lead to dysregulated autophagy and mitophagy. Here, we report that an ALS-associated TBK1 variant affecting the kinase domain, p.G175S, is defective in phosphorylation of p62 at Ser-403, a modification critical for regulating its ubiquitin-binding function, as well as downstream phosphorylation at Ser-349. Consistent with these findings, expression of p.G175S TBK1 was associated with decreased induction of autophagy compared to wild type and reduced degradation of the ALS-linked protein TDP-43. Expression of wild type TBK1 increased NF-κB signalling ~300 fold in comparison to empty vector cells, whereas p.G175S TBK1 was unable to promote NF-κB signalling above levels observed in empty vector transfected cells. We also noted a hitherto unknown role for TBK1 as a suppressor of oxidative stress (Nrf2) signalling and show that p.G175S TBK1 expressing cells lose this inhibitory function. Our data suggest that TBK1 ALS mutations may broadly impair p62-mediated cell signalling, which ultimately may reduce neuronal survival, in addition TDP-43 was not efficiently degraded, together these effects may contribute to TBK1 mutation associated ALS and FTLD pathogenesis.

Increased Tau Phosphorylation in Motor Neurons From Clinically Pure Sporadic Amyotrophic Lateral Sclerosis Patients

Amyotrophic lateral sclerosis (ALS) is characterized by the progressive degeneration of motor neurons. There is a pathological and genetic link between ALS and frontotemporal lobar degeneration (FTLD). Although FTLD is characterized by abnormal phosphorylated tau deposition, it is unknown whether tau is phosphorylated in ALS motor neurons. Therefore, this study assessed tau epitopes that are commonly phosphorylated in FTLD, including serine 396 (pS396), 214 (pS214), and 404 (pS404) in motor neurons from clinically pure sporadic ALS cases compared with controls. In ALS lower motor neurons, tau pS396 was observed in the nucleus or the nucleus and cytoplasm. In ALS upper motor neurons, tau pS396 was observed in the nucleus, cytoplasm, or both the nucleus and cytoplasm. Tau pS214 and pS404 was observed only in the cytoplasm of upper and lower motor neurons in ALS. The number of motor neurons (per mm2) positive for tau pS396 and pS214, but not pS404, was significantly increased in ALS. Furthermore, there was a significant loss of phosphorylated tau-negative motor neurons in ALS compared with controls. Together, our data identified a complex relationship between motor neurons positive for tau phosphorylated at specific residues and disease duration, suggesting that tau phosphorylation plays a role in ALS.

The role of sequestosome 1/p62 protein in amyotrophic lateral sclerosis and frontotemporal dementia pathogenesis

Amyotrophic lateral sclerosis and frontotemporal lobar degeneration are multifaceted diseases with genotypic, pathological and clinical overlap. One such overlap is the presence of SQSTM1/p62 mutations. While traditionally mutations manifesting in the ubiquitin-associated domain of p62 were associated with Paget’s disease of bone, mutations affecting all functional domains of p62 have now been identified in amyotrophic lateral sclerosis and frontotemporal lobar degeneration patients. p62 is a multifunctional protein that facilitates protein degradation through autophagy and the ubiquitin-proteasome system, and also regulates cell survival via the Nrf2 antioxidant response pathway, the nuclear factor-kappa B signaling pathway and apoptosis. Dysfunction in these signaling and protein degradation pathways have been observed in amyotrophic lateral sclerosis and frontotemporal lobar degeneration, and mutations that affect the role of p62 in these pathways may contribute to disease pathogenesis. In this review we discuss the role of p62 in these pathways, the effects of p62 mutations and the effect of mutations in the p62 modulator TANK-binding kinase 1, in relation to amyotrophic lateral sclerosis-frontotemporal lobar degeneration pathogenesis.

Pathogenic Tau Protein Species: Promising Therapeutic Targets for Ocular Neurodegenerative Diseases

Tau is a microtubule-associated protein, which is highly expressed in the central nervous system as well as ocular neurons and stabilizes microtubule structure. It is a phospho-protein being moderately phosphorylated under physiological conditions but its abnormal hyperphosphorylation or some post-phosphorylation modifications would result in a pathogenic condition, microtubule dissociation, and aggregation. The aggregates can induce neuroinflammation and trigger some pathogenic cascades, leading to neurodegeneration. Taking these together, targeting pathogenic tau employing tau immunotherapy may be a promising therapeutic strategy in fighting with cerebral and ocular neurodegenerative disorders.

Impact of traumatic brain injury on amyotrophic lateral sclerosis: from bedside to bench

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by the loss of upper and lower motor neurons, which manifests clinically as progressive weakness. Although several epidemiological studies have found an association between traumatic brain injury (TBI) and ALS, there is not a consensus on whether TBI is an ALS risk factor. It may be that it can cause ALS in a subset of susceptible patients, based on a history of repetitive mild TBI and genetic predisposition. This cannot be determined based on clinical observational studies alone. Better preclinical models are necessary to evaluate the effects of TBI on ALS onset and progression. To date, only a small number of preclinical studies have been performed, mainly in the superoxide dismutase 1 transgenic rodents, which, taken together, have mixed results and notable methodological limitations. The more recent incorporation of additional animal models such as Drosophila flies, as well as patient-induced pluripotent stem cell-derived neurons, should facilitate a better understanding of a potential functional interaction between TBI and ALS.

Phosphorylation of Threonine 175 Tau in the Induction of Tau Pathology in Amyotrophic Lateral Sclerosis-Frontotemporal Spectrum Disorder (ALS-FTSD). A Review

Approximately 50–60% of all patients with amyotrophic lateral sclerosis (ALS) will develop a deficit of frontotemporal function, ranging from frontotemporal dementia (FTD) to one or more deficits of neuropsychological, speech or language function which are collectively known as the frontotemporal spectrum disorders of ALS (ALS-FTSD). While the neuropathology underlying these disorders is most consistent with a widespread alteration in the metabolism of transactive response DNA-binding protein 43 (TDP-43), in both ALS with cognitive impairment (ALSci) and ALS with FTD (ALS-FTD; also known as MND-FTD) there is evidence for alterations in the metabolism of the microtubule associated protein tau. This alteration in tau metabolism is characterized by pathological phosphorylation at residue Thr¹⁷⁵ (pThr¹⁷⁵ tau) which in vitro is associated with activation of GSK3β (pTyr²¹⁶GSK3β), phosphorylation of Thr²³¹tau, and the formation of cytoplasmic inclusions with increased rates of cell death. This putative pathway of pThr¹⁷⁵ induction of pThr²³¹ and the formation of pathogenic tau inclusions has been recently shown to span a broad range of tauopathies, including chronic traumatic encephalopathy (CTE) and CTE in association with ALS (CTE-ALS). This pathway can be experimentally triggered through a moderate traumatic brain injury, suggesting that it is a primary neuropathological event and not secondary to a more widespread neuronal dysfunction. In this review, we discuss the neuropathological underpinnings of the postulate that ALS is associated with a tauopathy which manifests as a FTSD, and examine possible mechanisms by which phosphorylation at Thr¹⁷⁵tau is induced. We hypothesize that this might lead to an unfolding of the hairpin structure of tau, activation of GSK3β and pathological tau fibril formation through the induction of cis-Thr²³¹ tau conformers. A potential role of TDP-43 acting synergistically with pathological tau metabolism is proposed.

Synapse loss in the prefrontal cortex is associated with cognitive decline in amyotrophic lateral sclerosis

In addition to motor neurone degeneration, up to 50% of amyotrophic lateral sclerosis (ALS) patients present with cognitive decline. Understanding the neurobiological changes underlying these cognitive deficits is critical, as cognitively impaired patients exhibit a shorter survival time from symptom onset. Given the pathogenic role of synapse loss in other neurodegenerative diseases in which cognitive decline is apparent, such as Alzheimer’s disease, we aimed to assess synaptic integrity in the ALS brain. Here, we have applied a unique combination of high-resolution imaging of post-mortem tissue with neuropathology, genetic screening and cognitive profiling of ALS cases. Analyses of more than 1 million synapses using two complimentary high-resolution techniques (electron microscopy and array tomography) revealed a loss of synapses from the prefrontal cortex of ALS patients. Importantly, synapse loss was significantly greater in cognitively impaired cases and was not due to cortical atrophy, nor associated with dementia-associated neuropathology. Interestingly, we found a trend between pTDP-43 pathology and synapse loss in the frontal cortex and discovered pTDP-43 puncta at a subset of synapses in the ALS brains. From these data, we postulate that synapse loss in the prefrontal cortex represents an underlying neurobiological substrate of cognitive decline in ALS.

Possible concurrence of TDP-43, tau and other proteins in amyotrophic lateral sclerosis/frontotemporal lobar degeneration

Transactivation response DNA-binding protein 43 kDa (TDP-43) has been regarded as a major component of ubiquitin-positive/tau-negative inclusions of motor neurons and the frontotemporal cortices in amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD). Neurofibrillary tangles (NFT), an example of tau-positive inclusions, are biochemically and morphologically distinguished from TDP-43-positive inclusions, and are one of the pathological core features of Alzheimer disease (AD). Although ALS/FTLD and AD are distinct clinical entities, they can coexist in an individual patient. Whether concurrence of ALS/FTLD-TDP-43 and AD-tau is incidental is still controversial, because aging is a common risk factor for ALS/FTLD and AD development. Indeed, it remains unclear whether the pathogenesis of ALS/FTLD is a direct causal link to tau accumulation. Recent studies suggested that AD pathogenesis could cause the accumulation of TDP-43, while abnormal TDP-43 accumulation could also lead to abnormal tau expression. Overlapping presence of TDP-43 and tau, when observed in a brain during autopsy, should attract attention, and should initiate the search for the pathological substrate for this abnormal protein accumulation. In addition to tau, other proteins including α-synuclein and amyloid β should be also taken into account as candidates for an interaction with TDP-43. Awareness of a possible comorbidity between TDP-43, tau and other proteins in patients with ALS/FTLD will be useful for our understanding of the influence of these proteins on the disease development and its clinical manifestation.

Intrafamilial phenotypic heterogeneity in a Taiwanese family with a MAPT p.R5H mutation: a case report and literature review

Background

Frontotemporal degeneration (FTD) is a clinically and genetically heterogeneous neurodegenerative disorder characterized by deficits in executive function that frequently overlaps with parkinsonism and motor neuron disorders. Several genes have been identified to cause autosomal dominant forms of FTD, including the gene coding for the protein associated with microtubule tau (MAPT). While most reported pathogenic mutations in MAPT occur in exons 9–13, few families have been reported with mutations outside of this region. Herein, we report a first Taiwanese family having the exon 1 p.Arg5His mutation in MAPT with intrafamilial phenotype heterogeneity.

Case presentation

A 63-year-old man presented with progressive non-fluent speech and impaired memory for 3 years. He then developed apraxia, myoclonus and parkinsonism feature at his right hand. Extensive neurologic and neurocognitive examination lead to a diagnosis of FTD mixed with corticobasal syndrome. Magnetic resonance imaging revealed asymmetric atrophy in the left frontal and temporal lobes and single-photon emission computed tomography indicated decreased metabolism in the same areas as well as the left basal ganglia. The patient’s mother had been diagnosed with amyotrophic lateral sclerosis (ALS) at the age of 60 and was deceased 10 years later due to respiratory failure. The patient’s younger sister had persistent depressive disorder in her early forties and did not have any prominent cognitive or motor dysfunctions. We performed genetic analysis applying a targeted next generation sequencing (NGS) panel covering MAPT, GRN, VCP, FUS, CHMP2B, and TARDBP on the proband, followed by Sanger sequencing of candidate genes in eight family members. Hexanucleotide repeat expansion of C9Orf72 was determined by repeat-primed PCR. We identified a missense mutation in exon 1 of MAPT gene, c.14G > A (p.R5H), which was previously reported in only two Japanese patients in a literature review. This substitution co-segregated with the disease phenotypes in the family.

Conclusions

This is the first report of the occurrence of the MAPT p.R5H mutation in the Taiwanese population. Our findings extend the current knowledge of phenotypic heterogeneity among family members carrying the MAPT p.R5H mutation.

N-Acetyl-l-Cysteine Protects Astrocytes against Proteotoxicity without Recourse to Glutathione

N-acetyl-l-cysteine (NAC) exhibits protective properties in brain injury models and has undergone a number of clinical trials. Most studies of NAC have focused on neurons. However, neuroprotection may be complemented by the protection of astrocytes because healthier astrocytes can better support the viability of neurons. Here, we show that NAC can protect astrocytes against protein misfolding stress (proteotoxicity), the hallmark of neurodegenerative disorders. Although NAC is thought to be a glutathione precursor, NAC protected primary astrocytes from the toxicity of the proteasome inhibitor MG132 without eliciting any increase in glutathione. Furthermore, glutathione depletion failed to attenuate the protective effects of NAC. MG132 elicited a robust increase in the folding chaperone heat shock protein 70 (Hsp70), and NAC mitigated this effect. Nevertheless, three independent inhibitors of Hsp70 function ablated the protective effects of NAC, suggesting that NAC may help preserve Hsp70 chaperone activity and improve protein quality control without need for Hsp70 induction. Consistent with this view, NAC abolished an increase in ubiquitinated proteins in MG132-treated astrocytes. However, NAC did not affect the loss of proteasome activity in response to MG132, demonstrating that it boosted protein homeostasis and cell viability without directly interfering with the efficacy of this proteasome inhibitor. The thiol-containing molecules l-cysteine and d-cysteine both mimicked the protective effects of NAC, whereas the thiol-lacking molecule N-acetyl-S-methyl-l-cysteine failed to exert protection or blunt the rise in ubiquitinated proteins. Collectively, these findings suggest that the thiol group in NAC is required for its effects on glial viability and protein quality control.

Threonine175, a novel pathological phosphorylation site on tau protein linked to multiple tauopathies

Microtubule associated protein tau (tau) deposition is associated with a spectrum of neurodegenerative diseases collectively termed tauopathies. We have previously shown that amyotrophic lateral sclerosis (ALS) with cognitive impairment (ALSci) is associated with tau phosphorylation at Thr¹⁷⁵ and that this leads to activation of GSK3β which then induces phosphorylation at tau Thr²³¹. This latter step leads to dissociation of tau from microtubules and pathological tau fibril formation. To determine the extent to which this pathway is unique to ALS, we have investigated the expression of pThr¹⁷⁵ tau and pThr²³¹ tau across a range of frontotemporal degenerations. Representative sections from the superior frontal cortex, anterior cingulate cortex (ACC), amygdala, hippocampal formation, basal ganglia, and substantia nigra were selected from neuropathologically confirmed cases of Alzheimer’s disease (AD; n = 3), vascular dementia (n = 2), frontotemporal lobar degeneration (FTLD; n = 4), ALS (n = 5), ALSci (n = 6), Parkinson’s disease (PD; n = 5), corticobasal degeneration (CBD; n = 2), diffuse Lewy body dementia (DLBD; n = 2), mixed DLBD (n = 3), multisystem atrophy (MSA; n = 6) and Pick’s disease (n = 1) and three neuropathologically-normal control groups aged 50–60 (n = 6), 60–70 (n = 6) and 70–80 (n = 8). Sections were examined using a panel of phospho-tau antibodies (pSer^208,210, pThr²¹⁷, pThr¹⁷⁵, pThr²³¹, pSer²⁰² and T22 (oligomeric tau)). Across diseases, phospho-tau load was most prominent in layers II/III of the entorhinal cortex, amygdala and hippocampus. This is in contrast to the preferential deposition of phospho-tau in the ACC and frontal cortex in ALSci. Controls showed pThr¹⁷⁵ tau expression only in the 7^th decade of life and only in the presence of tau pathology and tau oligomers. With the exception of DLBD, we observed pThr¹⁷⁵ co-localizing with pThr²³¹ in the same cell populations as T22 positivity. This suggests that this pathway may be a common mechanism of toxicity across the tauopathies.

The Neurotoxic TAU45-230 Fragment Accumulates in Upper and Lower Motor Neurons in Amyotrophic Lateral Sclerosis Subjects

Amyotrophic lateral sclerosis (ALS) is a progressive and lethal neurodegenerative disease characterized by the loss of upper and lower motor neurons leading to muscle paralysis in affected individuals. Numerous mechanisms have been implicated in the death of these neurons. However, the pathobiology of this disease has not been completely elucidated. In the present study, we investigated to what extent tau cleavage and the generation of the neurotoxic tau45-230 fragment is associated with ALS. Quantitative Western blot analysis indicated that high levels of tau45-230 accumulated in lumbar and cervical spinal cord specimens obtained from ALS subjects. This neurotoxic tau fragment was also detected in ALS upper motor neurons located in the precentral gyrus. Our results also showed that tau45-230 aggregates were present in the spinal cord of ALS patients. On the other hand, this neurotoxic fragment was not generated in a mouse model of a familial form of this disease. Together, these results suggest a potential role for this neurotoxic tau fragment in the mechanisms leading to the degeneration of motor neurons in the context of sporadic ALS.

Astrocytes Surviving Severe Stress Can Still Protect Neighboring Neurons from Proteotoxic Injury

Astrocytes are one of the major cell types to combat cellular stress and protect neighboring neurons from injury. In order to fulfill this important role, astrocytes must sense and respond to toxic stimuli, perhaps including stimuli that are severely stressful and kill some of the astrocytes. The present study demonstrates that primary astrocytes that managed to survive severe proteotoxic stress were protected against subsequent challenges. These findings suggest that the phenomenon of preconditioning or tolerance can be extended from mild to severe stress for this cell type. Astrocytic stress adaptation lasted at least 96 h, the longest interval tested. Heat shock protein 70 (Hsp70) was raised in stressed astrocytes, but inhibition of neither Hsp70 nor Hsp32 activity abolished their resistance against a second proteotoxic challenge. Only inhibition of glutathione synthesis abolished astrocytic stress adaptation, consistent with our previous report. Primary neurons were plated upon previously stressed astrocytes, and the cocultures were then exposed to another proteotoxic challenge. Severely stressed astrocytes were still able to protect neighboring neurons against this injury, and the protection was unexpectedly independent of glutathione synthesis. Stressed astrocytes were even able to protect neurons after simultaneous application of proteasome and Hsp70 inhibitors, which otherwise elicited synergistic, severe loss of neurons when applied together. Astrocyte-induced neuroprotection against proteotoxicity was not elicited with astrocyte-conditioned media, suggesting that physical cell-to-cell contacts may be essential. These findings suggest that astrocytes may adapt to severe stress so that they can continue to protect neighboring cell types from profound injury.

Tau downregulates BDNF expression in animal and cellular models of Alzheimer's disease

In Alzheimer's disease, soluble tau accumulates and deposits as neurofibrillary tangles (NFTs). However, a precise toxic mechanism of tau is not well understood. We hypothesized that overexpression of wild-type tau downregulates brain-derived neurotrophic factor (BDNF), a neurotrophic peptide essential for learning and memory. Two transgenic mouse models of human tau expression and human tau (hTau40)-transfected human neuroblastoma (SH-SY5Y) cells were used to examine the effect of excess or pathologically modified wild-type human tau on BDNF expression. Both transgenic mouse models, with or without NFTs, as well as hTau40-SH-SY5Y cells significantly downregulated BDNF messenger RNA compared with controls. Similarly, transgenic mice overexpressing amyloid-β (Aβ) significantly downregulated BDNF expression. However, when crossed with tau knockout mice, the resulting animals exhibited BDNF levels that were not statistically different from wild-type mice. These results demonstrate that excess or pathologically modified wild-type human tau downregulates BDNF and that neither a mutation in tau nor the presence of NFTs is required for toxicity. Moreover, our findings suggest that tau at least partially mediates Aβ-induced BDNF downregulation. Therefore, Alzheimer's disease treatments targeting Aβ alone may not be effective without considering the impact of tau pathology on neurotrophic pathways.

Inside out: the role of nucleocytoplasmic transport in ALS and FTLD

Neurodegenerative diseases are characterized by the presence of protein inclusions with a different protein content depending on the type of disease. Amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD) are no exceptions to this common theme. In most ALS and FTLD cases, the predominant pathological species are RNA-binding proteins. Interestingly, these proteins are both depleted from their normal nuclear localization and aggregated in the cytoplasm. This key pathological feature has suggested a potential dual mechanism with both nuclear loss of function and cytoplasmic gain of function being at play. Yet, why and how this pathological cascade is initiated in most patients, and especially sporadic cases, is currently unresolved. Recent breakthroughs in C9orf72 ALS/FTLD disease models point at a pivotal role for the nuclear transport system in toxicity. To address whether defects in nuclear transport are indeed implicated in the disease, we reviewed two decades of ALS/FTLD literature and combined this with bioinformatic analyses. We find that both RNA-binding proteins and nuclear transport factors are key players in ALS/FTLD pathology. Moreover, our analyses suggest that disturbances in nucleocytoplasmic transport play a crucial initiating role in the disease, by bridging both nuclear loss and cytoplasmic gain of functions. These findings highlight this process as a novel and promising therapeutic target for ALS and FTLD.

The selective anatomical vulnerability of ALS: 'disease-defining' and 'disease-defying' brain regions

A large multiparametric MRI study has been undertaken to evaluate anatomical patterns of basal ganglia, white matter and cortical grey matter involvement in ALS. Unaffected brain regions are mapped in patients with significant disability. Multiple white matter diffusivity measures, cortical grey matter density alterations, basal ganglia volumes and subcortical grey matter atrophy patterns are evaluated. Results demonstrated a strikingly selective anatomical vulnerability pattern in ALS that preferentially affects specific grey matter structures, commissural white matter tracts and basal ganglia regions, suggestive of networkwise neurodegeneration in ALS. In conclusion, ALS pathology exhibits predilection for selective and inter-connected anatomical sites that can be comprehensively characterized in vivo by multiparametric neuroimaging. The systematic characterization of unaffected brain regions in ALS has implications for the development of classifier analyses and elucidation of disease biology. The involvement and sparing of contiguous brain regions raises important pathophysiological, phylogenetic and ontogenetic questions regarding ALS pathogenesis and disease spread.

Frontotemporal Dysfunction and Dementia in Amyotrophic Lateral Sclerosis

Although amyotrophic lateral sclerosis (ALS) is classically considered a disorder exclusively affecting motor neurons, there is substantial clinical, neuroimaging, and neuropathologic evidence that more than half of patients have an associated syndrome of frontotemporal dysfunction. These syndromes range from frontotemporal dementia to behavioral or cognitive syndromes. Neuroimaging and neuropathologic findings are consistent with frontotemporal lobar degeneration that underpins alterations in network connectivity. Future clinical trials need to be stratified based on the presence or absence of frontotemporal dysfunction on the disease course of ALS.

An Assessment of Possible Neuropathology and Clinical Relationships in 46 Sporadic Amyotrophic Lateral Sclerosis Patient Autopsies

BACKGROUND

Recent studies have suggested overlapping pathological features among motor neuron, cognitive and neurodegenerative diseases.

AIMS/METHODS

Secondary analysis of 46 amyotrophic lateral sclerosis (ALS) patient autopsies was performed to independently assess pathological feature prevalence (e.g. percent of patients with any positive finding), degree of severity (e.g. mild, moderate, severe), and 2,200+ potential clinical/neuropathological correlations. The possible impact of gender, onset age, onset type (limb vs. bulbar), riluzole treatment, and severe TDP-43 pathology was assessed within patient subgroups.

RESULTS

Assessed features (prevalence, severity) include: lateral corticospinal tract degeneration (89%, moderate); Purkinje cell loss (85%, mild); localized neuronal loss (83%, mild to moderate); TDP-43 inclusions (80%, moderate); Betz cell loss (76%, mild); neurofibrillary tangles (78%, severe); anterior corticospinal tract degeneration (72%, moderate); spinal ventral root atrophy (65%, moderate); atherosclerosis (35%, mild); β-amyloid (35%, mild); tauopathy/tau inclusions (17%, mild); ventricular dilation (13%, mild); Lewy body formation (11%, mild); microinfarcts (7%, mild); and α-synuclein (4%, mild). Twenty-two percent of patients met criteria for Alzheimer's disease (AD) and 26% for frontotemporal lobar degeneration. Substantial differences were identified in the AD group and in the different onset age groups.

CONCLUSION

Our findings support the hypothesis that ALS and its variants could comprise a larger neuropathological continuum.

Thr175-phosphorylated tau induces pathologic fibril formation via GSK3β-mediated phosphorylation of Thr231 in vitro

We have previously shown that amyotrophic lateral sclerosis with cognitive impairment can be characterized by pathologic inclusions of microtubule-associated protein tau (tau) phosphorylated at Thr(175) (pThr(175)) in association with GSK3β activation. We have now examined whether pThr(175) induces GSK3β activation and whether this leads to pathologic fibril formation through Thr(231) phosphorylation. Seventy-two hours after transfection of Neuro2A cells with pseudophosphorylated green fluorescent protein-tagged 2N4R tau (Thr(175)Asp), phosphorylated kinase glycogen synthase kinase 3 beta (active GSK3β) levels were significantly increased as was pathologic fibril formation and cell death. Treatment with each of 4 GSK3β inhibitors or small hairpin RNA knockdown of GSK3β abolished fibril formation and prevented cell death. Inhibition of Thr(231) phosphorylation (Thr(231)Ala) prevented pathologic tau fibril formation, regardless of Thr(175) state, whereas Thr(231)Asp (pseudophosphorylated at Thr(231)) developed pathologic tau fibrils. Ser(235) mutations did not affect fibril formation, indicating an unprimed mechanism of Thr(231) phosphorylation. These findings suggest a mechanism of tau pathology by which pThr(175) induces GSK3β phosphorylation of Thr(231) leading to fibril formation, indicating a potential therapeutic avenue for amyotrophic lateral sclerosis with cognitive impairment.

Astrocyte plasticity revealed by adaptations to severe proteotoxic stress

Neurodegeneration is characterized by an accumulation of misfolded proteins in neurons. It is less well appreciated that glia often also accumulate misfolded proteins. However, glia are highly plastic and may adapt to stress readily. Endogenous adaptations to stress can be measured by challenging stressed cells with a second hit and then measuring viability. For example, subtoxic stress can elicit preconditioning or tolerance against second hits. However, it is not known if severe stress that kills half the population can elicit endogenous adaptations in the remaining survivors. Glia, with their resilient nature, offer an ideal model in which to test this new hypothesis. The present study is the first demonstration that astrocytes surviving one LC50 hit of the proteasome inhibitor MG132 were protected against a second MG132 hit. ATP loss in response to the second hit was also prevented. MG132 caused compensatory rises in stress-sensitive heat shock proteins. However, stressed astrocytes exhibited an even greater rise in ubiquitin-conjugated proteins upon the second hit, illustrating the severity of the proteotoxicity and verifying the continued impact of MG132. Despite this stress, MG132-pretreated astrocytes were completely prevented from losing glutathione with the second hit. Furthermore, inhibiting glutathione synthesis rendered astrocytes sensitive to the second hit, unmasking the cumulative impact of two hits by removal of an endogenous adaptation. These findings suggest that stressed astrocytes become progressively harder to kill by virtue of antioxidant defenses. Such plasticity may permit astrocytes under severe stress to better support neurons and help explain the protracted nature of neurodegeneration.

Is the spinal cord motoneuron exclusively a target in ALS? Comparison between astroglial reactivity in a rat model of familial ALS and in human sporadic ALS cases

OBJECTIVE

Motoneurons are the focus of most investigations of amyotrophic lateral sclerosis (ALS), while the astrocyte reaction is regarded as a phenomenon secondary to neuron degeneration. Since astroglial reactivity differed in different studies of human and animal ALS models and often varied from case to case, we examined and compared astrocyte reactivity within the anterior horns of the spinal cord in a transgenic rat model of familial ALS and in human sporadic ALS (sALS) cases.

METHODS

Routine histological staining and immunohistochemical reactions to cytoskeletal proteins [neurofilaments, glial fibrillary acidic protein (GFAP), vimentin and tau] and proliferative markers (proliferating cell nuclear antigen and Ki-67).

RESULTS

In human sALS cases and in rats at the early pre-symptomatic and symptomatic stages of the disease, the astroglial reaction was very weak, although there was visible evidence of the morphological manifestations of motoneuron degeneration. Poor immunoreactivity to the GFAP and vimentin antigens and increased expression of tau protein were observed in astrocytes, particularly in the rat model. The astrocyte reaction was evident during a short ‘transient’ phase of the disease in animals, between the asymptomatic and paretic stages. Proliferating cell nuclear antigen immunoreactivity in glial and neuronal nuclei was observed only in animal material.

CONCLUSIONS

Abnormalities in astrocyte cytoskeletal proteins are characteristic features for ALS, both in acquired and congenital forms of the disease. The cytoskeletal aberrations may lead to astroglial dysfunction and disturbances in glutamate uptake that may in turn increase the degeneration of motoneurons.

Reduced protein O-glycosylation in the nervous system of the mutant SOD1 transgenic mouse model of amyotrophic lateral sclerosis

In the neurodegenerative disease amyotrophic lateral sclerosis (ALS), a number of proteins have been found to be hyperphosphorylated, including neurofilament proteins (NFs). In addition to protein phosphorylation, another important post-translational modification is O-glycosylation with β-N-acetylglucosamine residues (O-GlcNAc) and it has been found that O-GlcNAc can modify proteins competitively with protein phosphorylation, so that increased O-GlcNAc can reduce phosphorylation at specific sites. We evaluated a transgenic mouse model of ALS that overexpresses mutant superoxide dismutase (mSOD) and found that O-GlcNAc immunoreactivity levels are decreased in spinal cord tissue from mSOD mice, compared to controls. This reduction in O-GlcNAc levels is prominent in the motor neurons of spinal cord. We find that inhibition of O-GlcNAcase (OGA), the enzyme catalyzing removal of O-GlcNAc, using the inhibitor NButGT for 3 days, resulted in increased O-GlcNAc levels in spinal cord, both in mSOD and control mice. Furthermore, NButGT increased levels of O-GlcNAc modified NF-medium in spinal cords of control mice, but not in mSOD mice. These observations suggest that the neurodegeneration found in mSOD mice is associated with a reduction of O-GlcNAc levels in neurons, including motor neurons.

Widespread neuronal and glial hyperphosphorylated tau deposition in ALS with cognitive impairment

Although the biological basis of frontotemporal syndromes associated with amyotrophic lateral sclerosis (ALS) is considered to be altered metabolism of TDP-43, in ALS with cognitive impairment (ALSci) the metabolism of tau protein is also altered. This includes neuronal hyperphosphorylation (pThr(175)). Using novel polyclonal phospho-tau antibodies (pSer(208, 210), pThr(217) and pThr(175)) and antibodies directed against PHF tau (pSer(202)), TDP-43 or ubiquitin, we characterized tau deposition in ALS and ALSci. In ALS, we observed pThr(175) tau immunoreactive intraneuronal and neuritic aggregates throughout the amygdala and entorhinal cortex. In ALSci, this extended to the anterior cingulate gyrus, superior frontal cortex and substantia nigra. The pThr(217) antibody detected widespread astrocytic tau deposition, including punctuate or fibrillary aggregates, or intensely immunoreactive tufted astrocytes in the superior frontal cortex, anterior cingulate gyrus, entorhinal cortex, amygdala and basal ganglia of ALS. In ALSci, a similar but more widely distributed pThr(217) pathology was observed. There was no correlation between the extent of pathological tau deposition and TDP-43 pathology, although nuclear TDP-43 immunoreactivity was absent in neurons with tau pathology. In conclusion, ALSci is unique in possessing both tau and TDP-43 pathology. The presence of widespread astrocytic tau pathology suggests that ALSci may initially be characterized by astrocytic pathology.

Molecular pathology and genetic advances in amyotrophic lateral sclerosis: an emerging molecular pathway and the significance of glial pathology

Research into amyotrophic lateral sclerosis (ALS) has been stimulated by a series of genetic and molecular pathology discoveries. The hallmark neuronal cytoplasmic inclusions of sporadic ALS (sALS) predominantly comprise a nuclear RNA processing protein, TDP-43 encoded by the gene TARDBP, a discovery that emerged from high throughput analysis of human brain tissue from patients with frontotemporal dementia (FTD) who share a common molecular pathology with ALS. The link between RNA processing and ALS was further strengthened by the discovery that another genetic locus linking familial ALS (fALS) and FTD was due to mutation of the fused in sarcoma (FUS) gene. Of potentially even greater importance it emerges that TDP-43 accumulation and inclusion formation characterises not only most sALS cases but also those that arise from mutations in several genes including TARDBP (predominantly ALS cases) itself, C9ORF72 (ALS and FTD cases), progranulin (predominantly FTD phenotypes), VAPB (predominantly ALS cases) and in some ALS cases with rare genetic variants of uncertain pathogenicity (CHMP2B). "TDP-proteinopathy" therefore now represents a final common pathology associated with changes in multiple genes and opens the possibility of research by triangulation towards key common upstream molecular events. It also delivers final proof of the hypothesis that ALS and most FTD cases are disorders within a common pathology expressed as a clinico-anatomical spectrum. The emergence of TDP-proteinopathy also confirms the view that glial pathology is a crucial facet in this class of neurodegeneration, adding to the established view of non-nerve cell autonomous degeneration of the motor system from previous research on SOD1 fALS. Future research into the mechanisms of TDP-43 and FUS-related neurodegeneration, taking into account the major component of glial pathology now revealed in those disorders will significantly accelerate new discoveries in this field, including target identification for new therapy.

Expression of mutant TDP-43 induces neuronal dysfunction in transgenic mice

Background

Abnormal distribution, modification and aggregation of transactivation response DNA-binding protein 43 (TDP-43) are the hallmarks of multiple neurodegenerative diseases, especially frontotemporal lobar degeneration with ubiquitin-positive inclusions (FTLD-U) and amyotrophic lateral sclerosis (ALS). Researchers have identified 44 mutations in the TARDBP gene that encode TDP-43 as causative for cases of sporadic and familial ALS http://www.molgen.ua.ac.be/FTDMutations/. Certain mutant forms of TDP-43, such as M337V, are associated with increased low molecular weight (LMW) fragments compared to wild-type (WT) TDP-43 and cause neuronal apoptosis and developmental delay in chick embryos. Such findings support a direct link between altered TDP-43 function and neurodegeneration.

Results

To explore the pathogenic properties of the M337V mutation, we generated and characterized two mouse lines expressing human TDP-43 (hTDP-43_M337V) carrying this mutation. hTDP-43_M337V was expressed primarily in the nuclei of neurons in the brain and spinal cord, and intranuclear and cytoplasmic phosphorylated TDP-43 aggregates were frequently detected. The levels of TDP-43 LMW products of ~25 kDa and ~35 kDa species were also increased in the transgenic mice. Moreover, overexpression of hTDP-43_M337V dramatically down regulated the levels of mouse TDP-43 (mTDP-43) protein and RNA, indicating TDP-43 levels are tightly controlled in mammalian systems. TDP-43_M337V mice displayed reactive gliosis, widespread ubiquitination, chromatolysis, gait abnormalities, and early lethality. Abnormal cytoplasmic mitochondrial aggregates and abnormal phosphorylated tau were also detected in the mice.

Conclusion

Our novel TDP-43_M337V mouse model indicates that overexpression of hTDP-43_M337V alone is toxic in vivo. Because overexpression of hTDP-43 in wild-type TDP-43 and TDP-43_M337V mouse models produces similar phenotypes, the mechanisms causing pathogenesis in the mutant model remain unknown. However, our results suggest that overexpression of the hTDP-43_M337V can cause neuronal dysfunction due to its effect on a number of cell organelles and proteins, such as mitochondria and TDP-43, that are critical for neuronal activity. The mutant model will serve as a valuable tool in the development of future studies designed to uncover pathways associated with TDP-43 neurotoxicity and the precise roles TDP-43 RNA targets play in neurodegeneration.

Lack of effect of methylene blue in the SOD1 G93A mouse model of amyotrophic lateral sclerosis

Background

Methylene blue (MB) is a drug with a long history and good safety profile, and with recently-described features desirable in a treatment for ALS.

Methodology/Principal Findings

We tested oral MB in inbred high-copy number SOD1 G93A mice, at 25 mg/kg/day beginning at 45 days of age. We measured disease onset, progression, and survival. There was no difference in disease onset between MB-treated mice and controls, although subgroup analysis showed a modest but statistically significant delay in disease onset in MB-treated female mice only (control 122±10.2 versus MB 129±10.0 days). MB-treated mice of both sexes spent more time in less severe stages of disease, and less time in later, more severe stages of disease. There was a non-significant trend to longer survival in MB-treated animals (control males reached endpoint at 161±14.1 days, versus 166±10.0 days for MB-treated animals, and control females reached endpoint at 171±6.2 days versus 173±13.4 days for MB-treated animals).

Conclusions/Significance

In spite of a strong theoretical rationale, MB had no significant effects on onset or survival in the inbred SOD1 G93A mouse model of ALS.

The frontotemporal syndromes of ALS. Clinicopathological correlates

Amyotrophic lateral sclerosis (ALS) is increasingly recognized to be a syndromic disorder in which the degeneration of motor neurons is frequently accompanied by a range of syndromes reflective of frontotemporal dysfunction, including a behavioural or cognitive syndrome, a dysexecutive syndrome or a frontotemporal dementia. Both sporadic and familial variants of ALS can be affected. The anatomic substrate of each is a frontotemporal lobar degeneration (FTLD) characterized by superficial linear spongiosus, atrophy and neuronal loss, and both astrocytic and neuronal deposition of TDP-43 as pathological inclusions. Largely unrecognized however is the extent of alterations in tau protein metabolism, particularly in cognitively impaired patients (ALSci). This includes hyper-phosphorylation (pThr(175)) and tau phosphatase resistance, increased fibril formation ex vivo of tau isolated from ALSci and tau immunoreactive aggregates in neurons, dystrophic neurites and astrocytes. In this article, we will review the contemporary clinical, genetic and neuropathological characteristics of the frontotemporal syndromes of ALS and propose that as opposed to being a FTLD in which TDP-43 is the primary disease protein (FTLD-TDP) and that the frontotemporal syndromes of ALS represent a hybrid of both TDP-43 and tau pathology.

Mice with mutation in dynein heavy chain 1 do not share the same tau expression pattern with mice with SOD1-related motor neuron disease

Due to controversy about the involvement of Dync1h1 mutation in pathogenesis of motor neuron disease, we investigated expression of tau protein in transgenic hybrid mice with Dync1h1 (so-called Cra1/+), SOD1G93A (SOD1/+), double (Cra1/SOD1) mutations and wild-type controls. Total tau-mRNA and isoforms 0, 1 and 2 N expression was studied in frontal cortex, hippocampus, spinal cord and cerebellum of presymptomatic and symptomatic animals (age 70, 140 and 365 days). The most significant differences were found in brain cortex and cerebellum, but not in hippocampus and spinal cord. There were less changes in Cra1/SOD1 double heterozygotes compared to mice harboring single mutations. The differences in total tau expression and in profile of its isoforms between Cra1/+ and SOD1/+ transgenics indicate a distinct pathogenic entity of these two conditions.

Integrative gene-tissue microarray-based approach for identification of human disease biomarkers: application to amyotrophic lateral sclerosis

Advances in genomics and proteomics permit rapid identification of disease-relevant genes and proteins. Challenges include biological differences between animal models and human diseases, high discordance between DNA and protein expression data and a lack of experimental models to study human complex diseases. To overcome some of these limitations, we developed an integrative approach using animal models, postmortem human material and a combination of high-throughput microarray methods to identify novel molecular markers of amyotrophic lateral sclerosis (ALS). We used laser capture microdissection coupled with microarrays to identify early transcriptome changes occurring in spinal cord motor neurons or surrounding glial cells. Two models of familial motor neuron disease, SOD1(G93A) and TAU(P301L), transgenic mice were used at the presymptomatic stage. Identified gene expression changes were predominantly model-specific. However, several genes were regulated in both models. The relevance of identified genes as clinical biomarkers was tested in the peripheral blood transcriptome of presymptomatic SOD1(G93A) animals using custom-designed ALS microarray. To confirm the relevance of identified genes in human sporadic ALS (SALS), selected corresponding protein products were examined by high-throughput immunoassays using tissue microarrays constructed from human postmortem spinal cord tissues. Genes that were identified by these experiments and located within a linkage region associated with familial ALS/frontotemporal dementia were sequenced in several families. This large-scale gene and protein expression study pointing to distinct molecular mechanisms of TAU- and SOD1-induced motor neuron degeneration identified several new SALS-relevant proteins (CNGA3, CRB1, OTUB2, MMP14, SLK, DDX58, RSPO2) and putative blood biomarkers, including Nefh, Prph and Mgll.

Primary lateral sclerosis, hereditary spastic paraplegia and amyotrophic lateral sclerosis: Discrete entities or spectrum?

Among the motor neuron diseases, three share the clinical features of prominent upper motor neuron signs--amyotrophic lateral sclerosis (ALS), primary lateral sclerosis (PLS) and the hereditary spastic paraplegias (HSP). While genetic testing can assist in the identification of several variants of the latter, in the remaining cases, including those in which spasticity may be associated with amyotrophy, clinical differentiation of the three disorders may prove difficult. In this paper we review the evidence that these are distinct disorders and conclude that, for ALS and PLS particularly, there may be justification in considering them as single points along a continuum of multisystem disorders with conspicuous motor neuron involvement. Only through the development and application of exacting clinical diagnostic criteria to epidemiological studies, along with greater numbers of post-mortem examinations, however, will these questions be answered fully.

Targeting angiogenin in therapy of amyotropic lateral sclerosis

BACKGROUND

Missense heterozygous mutations in the coding region of angiogenin (ANG) gene, encoding a 14 kDa angiogenic RNase, were recently found in patients of amyotropic lateral sclerosis (ALS). Functional analyses have shown that these are loss-of-function mutations, implying that angiogenin deficiency is associated with ALS pathogenesis and that increasing ANG expression or angiogenin activity could be a novel approach for ALS therapy.

OBJECTIVE

Review the evidence showing the involvement of angiogenin in motor neuron physiology and function, and provide a rationale for targeting angiogenin in ALS therapy.

METHODS

Review the current understanding of the mechanism of angiogenin action in connection with ALS genetics, pathogenesis and therapy.

CONCLUSION

ANG is the first gene whose loss-of-function mutations are associated with ALS pathogenesis. Therapeutic modulation of angiogenin level and activity in the spinal cord, either by systemic delivery of angiogenin protein or through retrograde transport of ANG-encoding viral particles, may be beneficial for ALS patients.

Tau phosphorylation at threonine-175 leads to fibril formation and enhanced cell death: implications for amyotrophic lateral sclerosis with cognitive impairment

Although amyotrophic lateral sclerosis (ALS) can be associated with cognitive impairment (ALSci) as a reflection of frontotemporal lobar degeneration, the basis of this process is unknown. The observation of neuronal and extraneuronal tau deposition in ALSci in addition to a unique tau phosphorylation at Thr175 has suggested that ALSci can be associated with alterations in tau metabolism. We have examined the association between phosphorylation at Thr175 and tau fibril formation. Both soluble and insoluble tau was purified from control, patients with Alzheimer's disease (AD), ALS without cognitive impairment, and ALSci and the tendency to fibril formation assayed ex vivo using the thioflavin S fluorescence assay. The extent of fibril formation was significantly greater in tau derived from ALSci, with ALS-derived tau being intermediate between control and AD-derived tau. Using both Neuro2A and human embryonic kidney (HEK293T) cells, we expressed full-length tau constructs harboring either a pseudophosphorylation at Thr175 (Thr175-Asp-tau), inhibition of Thr175 phosphorylation (Thr175-Ala-tau) or intact tau (wild-type tau). Both tau fibril formation and cell death were significantly enhanced in the presence of Thr175-Asp-tau, regardless of the tau isoform, suggesting that phosphorylation of Thr175 is associated with tau fibril formation in ALSci.

p73 regulates neurodegeneration and phospho-tau accumulation during aging and Alzheimer's disease

The genetic mechanisms that regulate neurodegeneration are only poorly understood. We show that the loss of one allele of the p53 family member, p73, makes mice susceptible to neurodegeneration as a consequence of aging or Alzheimer's disease (AD). Behavioral analyses demonstrated that old, but not young, p73+/- mice displayed reduced motor and cognitive function, CNS atrophy, and neuronal degeneration. Unexpectedly, brains of aged p73+/- mice demonstrated dramatic accumulations of phospho-tau (P-tau)-positive filaments. Moreover, when crossed to a mouse model of AD expressing a mutant amyloid precursor protein, brains of these mice showed neuronal degeneration and early and robust formation of tangle-like structures containing P-tau. The increase in P-tau was likely mediated by JNK; in p73+/- neurons, the activity of the p73 target JNK was enhanced, and JNK regulated P-tau levels. Thus, p73 is essential for preventing neurodegeneration, and haploinsufficiency for p73 may be a susceptibility factor for AD and other neurodegenerative disorders.

Immunohistochemical study on the distribution of glycogen synthase kinase 3alpha in the central nervous system of SOD1(G93A) transgenic mice

OBJECTIVE

To identify glycogen synthase kinase (GSK) 3alpha expression in a mouse model of familial amyotrophic lateral sclerosis (ALS), we investigated the changes of GSK3alpha in the central nervous system of SOD1(G93A) transgenic mice by immunohistochemistry.

METHODS

We used 12 SOD1(G93A) transgenic and ten wild-type (wt) SOD1 transgenic mice bred by 'The Jackson Laboratory' under the strain designations B6SJL-TgN (SOD1(G93A)) 1 Gur/J and B6SJL-TgN (SOD1) 2 Gur/J, respectively. Immunohistochemistry was performed in accordance with the free-floating method described earlier.

RESULTS

In symptomatic transgenic mice, GSK3alpha-immunoreactive astrocytes were detected in the spinal cord, brainstem and cerebellum of symptomatic SOD1(G93A) transgenic mice. In contrast to symptomatic mice, no GSK3alpha-immunoreactive astrocytes were observed in any brain region of wtSOD1 and pre-symptomatic mice, and the number and intensity of stained cells were not different at the age of 8 and 13 weeks.

DISCUSSION

These results provide the first evidence that GSK3alpha-immunoreactive astrocytes were found in the CNS of SOD1(G93A) transgenic mice after clinical symptoms, suggesting a possible role in the pathologic process of ALS. However, the mechanisms underlying the increased immunoreactivity for GSK3alpha and the functional implications require elucidation.

Upregulation of GSK3beta expression in frontal and temporal cortex in ALS with cognitive impairment (ALSci)

The deposition of highly phosphorylated microtubule-associated tau protein has been observed in ALS with cognitive impairment (ALSci). In these studies, we have examined whether the expression of two candidate protein kinases for mediating tau hyperphosphorylation (GSK3beta or CDK5) are also altered. The expression of GSK, CDK and p25/p35 was assayed in human frontal, hippocampal, cerebellar, cervical (dorsal and ventral) and lumbar (dorsal and ventral) tissue from neurologically intact control (5), ALS (5) or ALSci (5) patients using RT-PCR, Western blot or immunohistochemistry. To assess GSK-3beta activity, we examined GSK3beta, phospho-GSK3beta and phospho-beta-catenin expression. Expression levels relative to that of beta-actin were compared by ANOVA. The expression of GSK, GSK3beta and phospho-GSK3beta was increased in both ALS and ALSci compared to that of the control. This was accompanied by an increased expression of phospho-beta-catenin. No significant difference between control, ALS or ALSci was observed with respect to the expression of CDK5 or p25/p35. Both GSK3beta and phospho-GSK3beta immunoreactive neurons were mainly located in layer II and layer III in the frontal cortex and in layer II in the hippocampus. This was consistent with the previously described distribution of hyperphosphorylated tau bearing neurons in ALS and ALSci. These data suggest that GSK3beta expression is upregulated in ALS and ALSci and that GSK3beta activation is associated with the intraneuronal deposition of hyperphosphorylated tau protein. This supports the potential role for GSK3beta as a therapeutic target in ALS.

Coexistence of amyotrophic lateral sclerosis and argyrophilic grain disease: a non-demented autopsy case showing circumscribed temporal atrophy and involvement of the amygdala

We report a case of a 68-year-old right-handed man with sporadic amyotrophic lateral sclerosis (ALS) and argyrophilic grain disease (AGD) having a 22-month duration. His initial symptoms were dysarthria and swallowing difficulty at the age of 67. Subsequently bulbar palsy and pyramidal signs developed. His cognitive functions including face recognition, personality, and behavior were not changed compared with that of before the disease onset. However, magnetic resonance imaging disclosed severe right side-predominant temporal atrophy. The neurological diagnosis was bulbar type ALS. Pathological examination disclosed histological evidence of ALS, including loss of Betz cells and lower motor neurons, corticospinal tract degeneration, and Bunina bodies. In addition, severe neuronal loss in the bilateral temporal cortex with an anterior gradient was found. Ubiquitin-positive inclusions were encountered in the spinal anterior horn cells and hippocampal dentate gyrus, while few ubiquitin-positive inclusions were noted in the affected temporal cortex. The amygdala, especially the basolateral nuclear group, was severely affected by neuronal loss with tissue rarefaction. Moderate neuronal loss was encountered in the parahippocampal gyrus, and to a lesser degree, in the ambient gyrus. Unexpectedly, many argyrophilic grains, coiled bodies, tau-positive bush-like astrocytes, pretangles, and ballooned neurons were found in the limbic system and temporal cortex. In the hippocampus, selective tau accumulation with minor neurofibrillary changes was observed in CA2 neurons. The present case suggests that (i) ALS and AGD do rarely coexist, and (ii) when ALS patients have severe temporal atrophy, not only ALS with dementia but also concurrent AGD should be considered in the differential diagnosis.

The tau N279K exon 10 splicing mutation recapitulates frontotemporal dementia and parkinsonism linked to chromosome 17 tauopathy in a mouse model

Intracellular tau deposits are characteristic of several neurodegenerative disorders called tauopathies. The tau protein regulates the stability and assembly of microtubules by binding to microtubules through three or four microtubule-binding repeats (3R and 4R). The number of microtubule-binding repeats is determined by the inclusion or exclusion of the second microtubule-binding repeat encoded by exon 10 of the TAU gene. TAU gene mutations that alter the inclusion of exon 10, and hence the 4R:3R ratio, are causal in the tauopathy frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17). A mutation located in exon 10 has been identified in several FTDP-17 families that present with increased exon 10 inclusion in both mRNA and protein, parkinsonism, movement disorders, and dementia. We have engineered a human tau minigene construct that was designed to allow alternative splicing of the tau exon 10. Here we demonstrate that transgenic mice expressing human tau protein with this mutation develop neurodegeneration as result of aberrant splicing. The mice recapitulate many of the disease hallmarks that are seen in patients with this mutation, including increased tau exon 10 inclusion in both mRNA and protein, motor and behavioral deficits, and tau protein accumulation in neurons and tufted astrocytes. Furthermore, these mice present with degeneration of the nigrostriatal dopaminergic pathway, suggesting a possible mechanism for parkinsonism in FTDP-17. Additionally, activated caspase-3 immunoreactivity in both neurons and astrocytes implicates the involvement of the apoptotic pathway in the pathology of these mice.