Clinical Significance of TDP-43 Neuropathology in Amyotrophic Lateral Sclerosis

Upper motor neuron-predominant motor neuron disease presenting as atypical parkinsonism: A clinicopathological study

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder characterized by upper and lower motor neuron signs. There are, however, cases where upper motor neurons (UMNs) are predominantly affected, leading to clinical presentations of UMN-dominant ALS or primary lateral sclerosis. Furthermore, cases exhibiting an UMN-predominant pattern of motor neuron disease (MND) presenting with corticobasal syndrome (CBS) have been sparsely reported. This study aims to clarify the clinicopathological features of patients with UMN-predominant MND. We reviewed 24 patients with UMN-predominant MND with TDP-43 pathology in the presence or absence of frontotemporal lobar degeneration. Additionally, we reviewed the medical records of patients with pathologically-confirmed corticobasal degeneration (CBD) who received a final clinical diagnosis of CBS (n = 10) and patients with pathologically-confirmed progressive supranuclear palsy (PSP) who received a final clinical diagnosis of PSP syndrome (n = 10). Of 24 UMN-predominant MND patients, 20 had a clinical diagnosis of an atypical parkinsonian disorder, including CBS (n = 11) and PSP syndrome (n = 8). Only two patients had antemortem diagnoses of motor neuron disease. UMN-predominant MND patients with CBS less frequently exhibited apraxia than those with CBD, and they were less likely to meet clinical criteria for possible or probable CBS. Similarly, UMN-predominant MND patients with PSP syndrome less often met clinical criteria for probable PSP than PSP patients with PSP syndrome. Our findings suggest that UMN-predominant MND can mimic atypical parkinsonism, and should be considered in the differential diagnosis of CBS and PSP syndrome, in particular when criteria are not met.

In vivo diagnosis of TDP-43 proteinopathies: in search of biomarkers of clinical use

TDP-43 proteinopathies are a heterogeneous group of neurodegenerative disorders that share the presence of aberrant, misfolded and mislocalized deposits of the protein TDP-43, as in the case of amyotrophic lateral sclerosis and some, but not all, pathological variants of frontotemporal dementia. In recent years, many other diseases have been reported to have primary or secondary TDP-43 proteinopathy, such as Alzheimer's disease, Huntington's disease or the recently described limbic-predominant age-related TDP-43 encephalopathy, highlighting the need for new and accurate methods for the early detection of TDP-43 proteinopathy to help on the stratification of patients with overlapping clinical diagnosis. Currently, TDP-43 proteinopathy remains a post-mortem pathologic diagnosis. Although the main aim is to determine the pathologic TDP-43 proteinopathy in the central nervous system (CNS), the ubiquitous expression of TDP-43 in biofluids and cells outside the CNS facilitates the use of other accessible target tissues that might reflect the potential TDP-43 alterations in the brain. In this review, we describe the main developments in the early detection of TDP-43 proteinopathies, and their potential implications on diagnosis and future treatments.

Cognitive function in amyotrophic lateral sclerosis: a cross-sectional and prospective pragmatic clinical study with review of the literature

BACKGROUND

Amyotrophic lateral sclerosis (ALS) can present with either bulbar or spinal symptoms, and in some cases, both types of symptoms may be present. In addition, cognitive impairment has been observed in ALS. The study aimed to evaluate the frontal and general cognitive performance in ALS not only cross-sectionally but also longitudinally.

METHODS AND MATERIALS

The Frontal Assessment Battery (FAB) and the Montreal Cognitive Assessment (MoCA) were employed to assess cognitive function in 52 adults with ALS and 52 cognitively healthy individuals. The statistical analyses encompassed the Pearson Chi square test, the Skillings-Mack test, the Spearman's rank correlation coefficient, and the Proportional Odds Logistic Regression Model (POLR).

RESULTS

Cross-sectionally, lower cognitive performance was associated with ALS diagnosis, older age, and motor functional decline. The cognitive impairment of individuals with bulbar and spinal-bulbar symptoms showed faster deterioration compared to those with spinal symptoms. The spinal subgroup consistently performed worst in delayed recall and attention, while the spinal-bulbar and bulbar subgroups exhibited inferior scores in delayed recall, attention, visuospatial skills, orientation, and verbal fluency.

CONCLUSION

The incorporation of cognitive screening in the diagnostic workup of ALS may be beneficial, as early detection can enhance symptom management and improve the quality of life for both individuals with ALS and their care partners.

Anterior insula is more vulnerable than posterior insula to TDP-43 pathology in common dementias and ALS

Based on the anatomic proximity, connectivity, and functional similarities between the anterior insula and amygdala, we tested the hypothesis that the anterior insula is an important focus in the progression of TDP-43 pathology in LATE-NC. Blinded to clinical and neuropathologic data, phospho-TDP (pTDP) inclusion pathology was assessed in paired anterior and posterior insula samples in 105 autopsied patients with Alzheimer disease, Lewy body disease, LATE-NC and hippocampal sclerosis (HS), amyotrophic lateral sclerosis (ALS), and other conditions. Insular pTDP pathology was present in 34.3% of the study cohort, most commonly as neuronal inclusions and/or short neurites in lamina II, and less commonly as subpial processes resembling those described in the amygdala region. Among positive samples, pTDP pathology was limited to the anterior insula (41.7%), or occurred in both anterior and posterior insula (58.3%); inclusion density was greater in anterior insula across all diseases (p < .001). pTDP pathology occurred in 46.7% of ALS samples, typically without a widespread TDP-43 proteinopathy. In LATE-NC, it was seen in 30.4% of samples (mostly LATE-NC stages 2 and 3), often co-occurring with basal forebrain pathology and comorbid HS, suggesting this is an important step in the evolution of this pathology beyond the medial temporal lobe.

Understanding depression with amyotrophic lateral sclerosis: a short assessment of facts and perceptions

Depression with an average prevalence of 25-40% is a serious condition in amyotrophic lateral sclerosis (ALS) that can impact quality of life and survival of patients and caregiver burden, yet the underlying neurobiology is poorly understood. Preexisting depression has been associated with a higher risk of developing ALS, while people with ALS have a significantly higher risk of developing depression that can cause multiple complications. Depression may be a prodromal or subclinical symptom prior to motor involvement, although its relations with disease progression and impairment of quality of life are under discussion. Unfortunately, there are no studies existing that explore the pathogenic mechanisms of depression associated with the basic neurodegenerative process, and no specific neuroimaging data or postmortem findings for the combination of ALS and depression are currently available. Experience from other neurodegenerative processes suggests that depressive symptoms in ALS may be the consequence of cortical thinning in prefrontal regions and other cortex areas, disruption of mood-related brain networks, dysfunction of neurotransmitter systems, changing cortisol levels and other, hitherto unknown mechanisms. Treatment of both ALS and depression is a multidisciplinary task, depression generally being treated with a combination of antidepressant medication, physiotherapy, psychological and other interventions, while electroconvulsive therapy and deep brain stimulation might not be indicated in the majority of patients in view of their poor prognosis. Since compared to depression in other neurodegenerative diseases, our knowledge of its molecular basis in ALS is missing, multidisciplinary clinicopathological studies to elucidate the pathomechanism of depression in motor system disorders including ALS are urgently warranted.

Primary visual cortex pathology in ALS patients with C9ORF72 expansion

Poly-GA and poly-GP immunofluorescence studies show conspicuous dipeptide repeat pathology in layers IV and II of primary visual cortex in C9ALS patients.

The Spectrum of Cognitive Dysfunction in Amyotrophic Lateral Sclerosis: An Update

Cognitive dysfunction is an important non-motor symptom in amyotrophic lateral sclerosis (ALS) that has a negative impact on survival and caregiver burden. It shows a wide spectrum ranging from subjective cognitive decline to frontotemporal dementia (FTD) and covers various cognitive domains, mainly executive/attention, language and verbal memory deficits. The frequency of cognitive impairment across the different ALS phenotypes ranges from 30% to 75%, with up to 45% fulfilling the criteria of FTD. Significant genetic, clinical, and pathological heterogeneity reflects deficits in various cognitive domains. Modern neuroimaging studies revealed frontotemporal degeneration and widespread involvement of limbic and white matter systems, with hypometabolism of the relevant areas. Morphological substrates are frontotemporal and hippocampal atrophy with synaptic loss, associated with TDP-43 and other co-pathologies, including tau deposition. Widespread functional disruptions of motor and extramotor networks, as well as of frontoparietal, frontostriatal and other connectivities, are markers for cognitive deficits in ALS. Cognitive reserve may moderate the effect of brain damage but is not protective against cognitive decline. The natural history of cognitive dysfunction in ALS and its relationship to FTD are not fully understood, although there is an overlap between the ALS variants and ALS-related frontotemporal syndromes, suggesting a differential vulnerability of motor and non-motor networks. An assessment of risks or the early detection of brain connectivity signatures before structural changes may be helpful in investigating the pathophysiological mechanisms of cognitive impairment in ALS, which might even serve as novel targets for effective disease-modifying therapies.

Artificial intelligence and statistical methods for stratification and prediction of progression in amyotrophic lateral sclerosis: A systematic review

BACKGROUND

Amyotrophic Lateral Sclerosis (ALS) is a fatal neurodegenerative disorder characterised by the progressive loss of motor neurons in the brain and spinal cord. The fact that ALS's disease course is highly heterogeneous, and its determinants not fully known, combined with ALS's relatively low prevalence, renders the successful application of artificial intelligence (AI) techniques particularly arduous.

OBJECTIVE

This systematic review aims at identifying areas of agreement and unanswered questions regarding two notable applications of AI in ALS, namely the automatic, data-driven stratification of patients according to their phenotype, and the prediction of ALS progression. Differently from previous works, this review is focused on the methodological landscape of AI in ALS.

METHODS

We conducted a systematic search of the Scopus and PubMed databases, looking for studies on data-driven stratification methods based on unsupervised techniques resulting in (A) automatic group discovery or (B) a transformation of the feature space allowing patient subgroups to be identified; and for studies on internally or externally validated methods for the prediction of ALS progression. We described the selected studies according to the following characteristics, when applicable: variables used, methodology, splitting criteria and number of groups, prediction outcomes, validation schemes, and metrics.

RESULTS

Of the starting 1604 unique reports (2837 combined hits between Scopus and PubMed), 239 were selected for thorough screening, leading to the inclusion of 15 studies on patient stratification, 28 on prediction of ALS progression, and 6 on both stratification and prediction. In terms of variables used, most stratification and prediction studies included demographics and features derived from the ALSFRS or ALSFRS-R scores, which were also the main prediction targets. The most represented stratification methods were K-means, and hierarchical and expectation-maximisation clustering; while random forests, logistic regression, the Cox proportional hazard model, and various flavours of deep learning were the most widely used prediction methods. Predictive model validation was, albeit unexpectedly, quite rarely performed in absolute terms (leading to the exclusion of 78 eligible studies), with the overwhelming majority of included studies resorting to internal validation only.

CONCLUSION

This systematic review highlighted a general agreement in terms of input variable selection for both stratification and prediction of ALS progression, and in terms of prediction targets. A striking lack of validated models emerged, as well as a general difficulty in reproducing many published studies, mainly due to the absence of the corresponding parameter lists. While deep learning seems promising for prediction applications, its superiority with respect to traditional methods has not been established; there is, instead, ample room for its application in the subfield of patient stratification. Finally, an open question remains on the role of new environmental and behavioural variables collected via novel, real-time sensors.

SBT-272 improves TDP-43 pathology in ALS upper motor neurons by modulating mitochondrial integrity, motility, and function

Mitochondrial defects are one of the common underlying causes of neuronal vulnerability in neurodegenerative diseases, such as amyotrophic lateral sclerosis (ALS), and TDP-43 pathology is the most commonly observed proteinopathy. Disrupted inner mitochondrial membrane (IMM) reported in the upper motor neurons (UMNs) of ALS patients with TDP-43 pathology is recapitulated in the UMNs of well-characterized hTDP-43 mouse model of ALS. The construct validity, such as shared and common cellular pathology in mice and human, offers a unique opportunity to test treatment strategies that may translate to patients. SBT-272 is a well-tolerated brain-penetrant small molecule that stabilizes cardiolipin, a phospholipid found in IMM, thereby restoring mitochondrial structure and respiratory function. We investigated whether SBT-272 can improve IMM structure and health in UMNs diseased with TDP-43 pathology in our well-characterized UMN reporter line for ALS. We found that SBT-272 significantly improved mitochondrial structural integrity and restored mitochondrial motility and function. This led to improved health of diseased UMNs in vitro. In comparison to edaravone and AMX0035, SBT-272 appeared more effective in restoring health of diseased UMNs. Chronic treatment of SBT-272 for sixty days starting at an early symptomatic stage of the disease in vivo led to a significant reduction in astrogliosis, microgliosis, and TDP-43 pathology in the ALS motor cortex. Our results underscore the therapeutic potential of SBT-272, especially within the context of TDP-43 pathology and mitochondrial dysfunction.

Neuropathology and neuroanatomy of TDP-43 amyotrophic lateral sclerosis

PURPOSE OF REVIEW

Intracellular inclusions consisting of the abnormal TDP-43 protein and its nucleocytoplasmic mislocalization in selected cell types are hallmark pathological features of sALS. Descriptive (histological, morphological), anatomical, and molecular studies all have improved our understanding of the neuropathology of sporadic amyotrophic lateral sclerosis (sALS). This review highlights some of the latest developments in the field.

RECENT FINDINGS

Increasing evidence exists from experimental models for the prion-like nature of abnormal TDP-43, including a strain-effect, and with the help of neuroimaging-based studies, for spreading of disease along corticofugal connectivities in sALS. Progress has also been made with respect to finding and establishing reliable biomarkers (neurofilament levels, diffusor tensor imaging).

SUMMARY

The latest findings may help to elucidate the preclinical phase of sALS and to define possible mechanisms for delaying or halting disease development and progression.

The Cell Autonomous and Non-Cell Autonomous Aspects of Neuronal Vulnerability and Resilience in Amyotrophic Lateral Sclerosis

Simple Summary

Amyotrophic lateral sclerosis (ALS) is a fatal disease characterized by a progressive paralysis due to the loss of particular neurons in our nervous system called motor neurons, that exert voluntary control of all our skeletal muscles. It is not entirely understood why motor neurons are particularly vulnerable in ALS, neither is it completely clear why certain groups of motor neurons, including those that regulate eye movement, are rather resilient to this disease. However, both vulnerability and resilience to ALS likely reflect cell intrinsic properties of different motor neuron subpopulations as well as non-cell autonomous events regulated by surrounding cell types. In this review we dissect the particular properties of different motor neuron types and their responses to disease that may underlie their respective vulnerabilities and resilience. Disease progression in ALS involves multiple cell types that are closely connected to motor neurons and we here also discuss their contributions to the differential vulnerability of motor neurons.

Abstract

Amyotrophic lateral sclerosis (ALS) is defined by the loss of upper motor neurons (MNs) that project from the cerebral cortex to the brain stem and spinal cord and of lower MNs in the brain stem and spinal cord which innervate skeletal muscles, leading to spasticity, muscle atrophy, and paralysis. ALS involves several disease stages, and multiple cell types show dysfunction and play important roles during distinct phases of disease initiation and progression, subsequently leading to selective MN loss. Why MNs are particularly vulnerable in this lethal disease is still not entirely clear. Neither is it fully understood why certain MNs are more resilient to degeneration in ALS than others. Brain stem MNs of cranial nerves III, IV, and VI, which innervate our eye muscles, are highly resistant and persist until the end-stage of the disease, enabling paralyzed patients to communicate through ocular tracking devices. MNs of the Onuf’s nucleus in the sacral spinal cord, that innervate sphincter muscles and control urogenital functions, are also spared throughout the disease. There is also a differential vulnerability among MNs that are intermingled throughout the spinal cord, that directly relate to their physiological properties. Here, fast-twitch fatigable (FF) MNs, which innervate type IIb muscle fibers, are affected early, before onset of clinical symptoms, while slow-twitch (S) MNs, that innervate type I muscle fibers, remain longer throughout the disease progression. The resilience of particular MN subpopulations has been attributed to intrinsic determinants and multiple studies have demonstrated their unique gene regulation and protein content in health and in response to disease. Identified factors within resilient MNs have been utilized to protect more vulnerable cells. Selective vulnerability may also, in part, be driven by non-cell autonomous processes and the unique surroundings and constantly changing environment close to particular MN groups. In this article, we review in detail the cell intrinsic properties of resilient and vulnerable MN groups, as well as multiple additional cell types involved in disease initiation and progression and explain how these may contribute to the selective MN resilience and vulnerability in ALS.

Utility of the ALSFRS-R for predicting ALS and comorbid disease neuropathology: The Veterans Affairs Biorepository Brain Bank

INTRODUCTION/AIMS

The amyotrophic lateral sclerosis (ALS) functional rating scale-revised (ALSFRS-R) is commonly used to track ALS disease progression; however, there are gaps in the literature regarding the extent to which the ALSFRS-R relates to underlying central nervous system (CNS) pathology. The current study explored the association between ALSFRS-R (total and subdomain) scores and postmortem neuropathology (both ALS-specific and comorbid disease).

METHODS

Within our sample of 93 military veterans with autopsy-confirmed ALS, we utilized hierarchical cluster analysis (HCA) to identify discrete profiles of motor dysfunction based on ALSFRS-R subdomain scores. We examined whether emergent clusters were associated with neuropathology. Separate analyses of variance and covariance with post-hoc comparisons were performed to examine relevant cluster differences.

RESULTS

Analyses revealed significant correlations between ALSFRS-R total and subdomain scores with some, but not all, neuropathological variables. The HCA illustrated three groups: Cluster 1-predominantly diffuse functional impairment; Cluster 2-spared respiratory/bulbar and impaired motor function; and Cluster 3-spared bulbar and impaired respiratory, and fine and gross motor function. Individuals in Cluster 1 (and to a lesser degree, Cluster 3) exhibited greater accumulation of ALS-specific neuropathology and less comorbid neuropathology than those in Cluster 2.

DISCUSSION

These results suggest that discrete patterns of motor dysfunction based on ALSFRS-R subdomain scores are related to postmortem neuropathology. Findings support use of ALSFRS-R subdomain scores to capture the heterogeneity of clinical presentation and disease progression in ALS, and may assist researchers in identifying endophenotypes for separate assessment in clinical trials.

Transactive Response DNA-Binding Protein (TARDBP/TDP-43) Regulates Cell Permissivity to HIV-1 Infection by Acting on HDAC6

The transactive response DNA-binding protein (TARDBP/TDP-43) influences the processing of diverse transcripts, including that of histone deacetylase 6 (HDAC6). Here, we assessed TDP-43 activity in terms of regulating CD4+ T-cell permissivity to HIV-1 infection. We observed that overexpression of wt-TDP-43 increased both mRNA and protein levels of HDAC6, resulting in impaired HIV-1 infection independently of the viral envelope glycoprotein complex (Env) tropism. Consistently, using an HIV-1 Env-mediated cell-to-cell fusion model, the overexpression of TDP-43 levels negatively affected viral Env fusion capacity. Silencing of endogenous TDP-43 significantly decreased HDAC6 levels and increased the fusogenic and infection activities of the HIV-1 Env. Using pseudovirus bearing primary viral Envs from HIV-1 individuals, overexpression of wt-TDP-43 strongly reduced the infection activity of Envs from viremic non-progressors (VNP) and rapid progressors (RP) patients down to the levels of the inefficient HIV-1 Envs observed in long-term non-progressor elite controllers (LTNP-EC). On the contrary, silencing endogenous TDP-43 significantly favored the infectivity of primary Envs from VNP and RP individuals, and notably increased the infection of those from LTNP-EC. Taken together, our results indicate that TDP-43 shapes cell permissivity to HIV-1 infection, affecting viral Env fusion and infection capacities by altering the HDAC6 levels and associated tubulin-deacetylase anti-HIV-1 activity.

Patterns of amygdala region pathology in LATE-NC: subtypes that differ with regard to TDP-43 histopathology, genetic risk factors, and comorbid pathologies

Transactive response (TAR) DNA-binding protein 43 kDa (TDP-43) pathology is a hallmark of limbic-predominant age-related TDP-43 encephalopathy (LATE). The amygdala is affected early in the evolution of LATE neuropathologic change (LATE-NC), and heterogeneity of LATE-NC in amygdala has previously been observed. However, much remains to be learned about how LATE-NC originates and progresses in the brain. To address this, we assessed TDP-43 and other pathologies in the amygdala region of 184 autopsied subjects (median age = 85 years), blinded to clinical diagnoses, other neuropathologic diagnoses, and risk genotype information. As previously described, LATE-NC was associated with older age at death, cognitive impairment, and the TMEM106B risk allele. Pathologically, LATE-NC was associated with comorbid hippocampal sclerosis (HS), myelin loss, and vascular disease in white matter (WM). Unbiased hierarchical clustering of TDP-43 inclusion morphologies revealed discernable subtypes of LATE-NC with distinct clinical, genetic, and pathologic associations. The most common patterns were: Pattern 1, with lamina II TDP-43 + processes and preinclusion pathology in cortices of the amygdala region, and frequent LATE-NC Stage 3 with HS; Pattern 2, previously described as type-β, with neurofibrillary tangle-like TDP-43 neuronal cytoplasmic inclusions (NCIs), high Alzheimer's disease neuropathologic change (ADNC), frequent APOE ε4, and usually LATE-NC Stage 2; Pattern 3, with round NCIs and thick neurites in amygdala, younger age at death, and often comorbid Lewy body disease; and Pattern 4 (the most common pattern), with tortuous TDP-43 processes in subpial and WM regions, low ADNC, rare HS, and lower dementia probability. TDP-43 pathology with features of patterns 1 and 2 were often comorbid in the same brains. Early and mild TDP-43 pathology was often best described to be localized in the "amygdala region" rather than the amygdala proper. There were also important shared attributes across patterns. For example, all four patterns were associated with the TMEM106B risk allele. Each pattern also demonstrated the potential to progress to higher LATE-NC stages with confluent anatomical and pathological patterns, and to contribute to dementia. Although LATE-NC showed distinct patterns of initiation in amygdala region, there was also apparent shared genetic risk and convergent pathways of clinico-pathological evolution.

Upper motor neurons are a target for gene therapy and UCHL1 is necessary and sufficient to improve cellular integrity of diseased upper motor neurons

There are no effective cures for upper motor neuron (UMN) diseases, such as amyotrophic lateral sclerosis (ALS), primary lateral sclerosis, and hereditary spastic paraplegia. Here, we show UMN loss occurs independent of spinal motor neuron degeneration and that UMNs are indeed effective cellular targets for gene therapy, which offers a potential solution especially for UMN disease patients. UCHL1 (ubiquitin C-terminal hydrolase-L1) is a deubiquitinating enzyme crucial for maintaining free ubiquitin levels. Corticospinal motor neurons (CSMN, a.k.a UMNs in mice) show early, selective, and profound degeneration in Uchl1nm3419 (UCHL1-/-) mice, which lack all UCHL1 function. When UCHL1 activity is ablated only from spinal motor neurons, CSMN remained intact. However, restoring UCHL1 specifically in CSMN of UCHL1-/- mice via directed gene delivery was sufficient to improve CSMN integrity to the healthy control levels. In addition, when UCHL1 gene was delivered selectively to CSMN that are diseased due to misfolded SOD1 toxicity and TDP-43 pathology via AAV-mediated retrograde transduction, the disease causing misfolded SOD1 and mutant human TDP-43 were reduced in hSOD1G93A and prpTDP-43A315T models, respectively. Diseased CSMN retained their neuronal integrity and cytoarchitectural stability in two different mouse models that represent two distinct causes of neurodegeneration in ALS.

An open source toolkit for repurposing Illumina sequencing systems as versatile fluidics and imaging platforms

Fluorescence microscopy is a key method in the life sciences. State of the art -omics methods combine fluorescence microscopy with complex protocols to visualize tens to thousands of features in each of millions of pixels across samples. These -omics methods require precise control of temperature, reagent application, and image acquisition parameters during iterative chemistry and imaging cycles conducted over the course of days or weeks. Automated execution of such methods enables robust and reproducible data generation. However, few commercial solutions exist for temperature controlled, fluidics coupled fluorescence imaging, and implementation of bespoke instrumentation requires specialized engineering expertise. Here we present PySeq2500, an open source Python code base and flow cell design that converts the Illumina HiSeq 2500 instrument, comprising an epifluorescence microscope with integrated fluidics, into an open platform for programmable applications without need for specialized engineering or software development expertise. Customizable PySeq2500 protocols enable experimental designs involving simultaneous 4-channel image acquisition, temperature control, reagent exchange, stable positioning, and sample integrity over extended experiments. To demonstrate accessible automation of complex, multi-day workflows, we use the PySeq2500 system for unattended execution of iterative indirect immunofluorescence imaging (4i). Our automated 4i method uses off-the-shelf antibodies over multiple cycles of staining, imaging, and antibody elution to build highly multiplexed maps of cell types and pathological features in mouse and postmortem human spinal cord sections. Given the widespread availability of HiSeq 2500 platforms and the simplicity of the modifications required to repurpose these systems, PySeq2500 enables non-specialists to develop and implement state of the art fluidics coupled imaging methods in a widely available benchtop system.

Pathophysiological Underpinnings of Extra-Motor Neurodegeneration in Amyotrophic Lateral Sclerosis: New Insights From Biomarker Studies

Amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD) lie at opposing ends of a clinical, genetic, and neuropathological continuum. In the last decade, it has become clear that cognitive and behavioral changes in patients with ALS are more frequent than previously recognized. Significantly, these non-motor features can impact the diagnosis, prognosis, and management of ALS. Partially overlapping neuropathological staging systems have been proposed to describe the distribution of TAR DNA-binding protein 43 (TDP-43) aggregates outside the corticospinal tract. However, the relationship between TDP-43 inclusions and neurodegeneration is not absolute and other pathophysiological processes, such as neuroinflammation (with a prominent role of microglia), cortical hyperexcitability, and synaptic dysfunction also play a central role in ALS pathophysiology. In the last decade, imaging and biofluid biomarker studies have revealed important insights into the pathophysiological underpinnings of extra-motor neurodegeneration in the ALS-FTLD continuum. In this review, we first summarize the clinical and pathophysiological correlates of extra-motor neurodegeneration in ALS. Next, we discuss the diagnostic and prognostic value of biomarkers in ALS and their potential to characterize extra-motor neurodegeneration. Finally, we debate about how biomarkers could improve the diagnosis and classification of ALS. Emerging imaging biomarkers of extra-motor neurodegeneration that enable the monitoring of disease progression are particularly promising. In addition, a growing arsenal of biofluid biomarkers linked to neurodegeneration and neuroinflammation are improving the diagnostic accuracy and identification of patients with a faster progression rate. The development and validation of biomarkers that detect the pathological aggregates of TDP-43 in vivo are notably expected to further elucidate the pathophysiological underpinnings of extra-motor neurodegeneration in ALS. Novel biomarkers tracking the different aspects of ALS pathophysiology are paving the way to precision medicine approaches in the ALS-FTLD continuum. These are essential steps to improve the diagnosis and staging of ALS and the design of clinical trials testing novel disease-modifying treatments.

Distinct patterns of progressive gray and white matter degeneration in amyotrophic lateral sclerosis

Progressive cerebral degeneration in amyotrophic lateral sclerosis (ALS) remains poorly understood. Here, three-dimensional (3D) texture analysis was used to study longitudinal gray and white matter cerebral degeneration in ALS from routine T1-weighted magnetic resonance imaging (MRI). Participants were included from the Canadian ALS Neuroimaging Consortium (CALSNIC) who underwent up to three clinical assessments and MRI at four-month intervals, up to 8 months after baseline (T₀ ). Three-dimensional maps of the texture feature autocorrelation were computed from T1-weighted images. One hundred and nineteen controls and 137 ALS patients were included, with 81 controls and 84 ALS patients returning for at least one follow-up. At baseline, texture changes in ALS patients were detected in the motor cortex, corticospinal tract, insular cortex, and bilateral frontal and temporal white matter compared to controls. Longitudinal comparison of texture maps between T₀ and T_max (last follow-up visit) within ALS patients showed progressive texture alterations in the temporal white matter, insula, and internal capsule. Additionally, when compared to controls, ALS patients had greater texture changes in the frontal and temporal structures at T_max than at T₀ . In subgroup analysis, slow progressing ALS patients had greater progressive texture change in the internal capsule than the fast progressing patients. Contrastingly, fast progressing patients had greater progressive texture changes in the precentral gyrus. These findings suggest that the characteristic longitudinal gray matter pathology in ALS is the progressive involvement of frontotemporal regions rather than a worsening pathology within the motor cortex, and that phenotypic variability is associated with distinct progressive spatial pathology.

Fast Progression in Amyotrophic Lateral Sclerosis Is Associated With Greater TDP-43 Burden in Spinal Cord

Upper and lower motor neuron pathologies are critical to the autopsy diagnosis of amyotrophic lateral sclerosis (ALS). Further investigation is needed to determine how the relative burden of these pathologies affects the disease course. We performed a blinded, retrospective study of 38 ALS patients, examining the association between pathologic measures in motor cortex, hypoglossal nucleus, and lumbar cord with clinical data, including progression rate and disease duration, site of symptom onset, and upper and lower motor neuron signs. The most critical finding in our study was that TAR DNA-binding protein 43 kDa (TDP-43) pathologic burden in lumbar cord and hypoglossal nucleus was significantly associated with a faster progression rate with reduced survival (p < 0.02). There was no correlation between TDP-43 burden and the severity of cell loss, and no significant clinical associations were identified for motor cortex TDP-43 burden or severity of cell loss in motor cortex. C9orf72 expansion was associated with shorter disease duration (p < 0.001) but was not significantly associated with pathologic measures in these regions. The association between lower motor neuron TDP-43 burden and fast progression with reduced survival in ALS provides further support for the study of TDP-43 as a disease biomarker.

Proteostatic imbalance and protein spreading in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder whose exact causative mechanisms are still under intense investigation. Several lines of evidence suggest that the anatomical and temporal propagation of pathological protein species along the neural axis could be among the main driving mechanisms for the fast and irreversible progression of ALS pathology. Many ALS-associated proteins form intracellular aggregates as a result of their intrinsic prion-like properties and/or following impairment of the protein quality control systems. During the disease course, these mutated proteins and aberrant peptides are released in the extracellular milieu as soluble or aggregated forms through a variety of mechanisms. Internalization by recipient cells may seed further aggregation and amplify existing proteostatic imbalances, thus triggering a vicious cycle that propagates pathology in vulnerable cells, such as motor neurons and other susceptible neuronal subtypes. Here, we provide an in-depth review of ALS pathology with a particular focus on the disease mechanisms of seeding and transmission of the most common ALS-associated proteins, including SOD1, FUS, TDP-43, and C9orf72-linked dipeptide repeats. For each of these proteins, we report historical, biochemical, and pathological evidence of their behaviors in ALS. We further discuss the possibility to harness pathological proteins as biomarkers and reflect on the implications of these findings for future research.

Neuroinflammation is highest in areas of disease progression in semantic dementia

Despite epidemiological and genetic data linking semantic dementia to inflammation, the topography of neuroinflammation in semantic dementia, also known as the semantic variant of primary progressive aphasia, remains unclear. The pathology starts at the tip of the left temporal lobe where, in addition to cortical atrophy, a strong signal appears with the tau PET tracer 18F-flortaucipir, even though the disease is not typically associated with tau but with TDP-43 protein aggregates. Here, we characterized the topography of inflammation in semantic variant primary progressive aphasia using high-resolution PET and the tracer 11C-PBR28 as a marker of microglial activation. We also tested the hypothesis that inflammation, by providing non-specific binding targets, could explain the 18F-flortaucipir signal in semantic variant primary progressive aphasia. Eight amyloid-PET-negative patients with semantic variant primary progressive aphasia underwent 11C-PBR28 and 18F-flortaucipir PET. Healthy controls underwent 11C-PBR28 PET (n = 12) or 18F-flortaucipir PET (n = 12). Inflammation in PET with 11C-PBR28 was analysed using Logan graphical analysis with a metabolite-corrected arterial input function. 18F-flortaucipir standardized uptake value ratios were calculated using the cerebellum as the reference region. Since monoamine oxidase B receptors are expressed by astrocytes in affected tissue, selegiline was administered to one patient with semantic variant primary progressive aphasia before repeating 18F-flortaucipir scanning to test whether monoamine oxidase B inhibition blocked flortaucipir binding, which it did not. While 11C-PBR28 uptake was mostly cortical, 18F-flortaucipir uptake was greatest in the white matter. The uptake of both tracers was increased in the left temporal lobe and in the right temporal pole, as well as in regions adjoining the left temporal pole such as insula and orbitofrontal cortex. However, peak uptake of 18F-flortaucipir localized to the left temporal pole, the epicentre of pathology, while the peak of inflammation 11C-PBR28 uptake localized to a more posterior, mid-temporal region and left insula and orbitofrontal cortex, in the periphery of the damage core. Neuroinflammation, greatest in the areas of progression of the pathological process in semantic variant primary progressive aphasia, should be further studied as a possible therapeutic target to slow disease progression.

Moving Toward Patient-Tailored Treatment in ALS and FTD: The Potential of Genomic Assessment as a Tool for Biological Discovery and Trial Recruitment

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are two devastating and intertwined neurodegenerative diseases. Historically, ALS and FTD were considered distinct disorders given differences in presenting clinical symptoms, disease duration, and predicted risk of developing each disease. However, research over recent years has highlighted the considerable clinical, pathological, and genetic overlap of ALS and FTD, and these two syndromes are now thought to represent different manifestations of the same neuropathological disease spectrum. In this review, we discuss the need to shift our focus from studying ALS and FTD in isolation to identifying the biological mechanisms that drive these diseases-both common and distinct-to improve treatment discovery and therapeutic development success. We also emphasize the importance of genomic data to facilitate a "precision medicine" approach for treating ALS and FTD.

Examining the Relationship between Concussion and Neurodegenerative Disorders: A Review on Amyotrophic Lateral Sclerosis (ALS) and Alzheimer’s Disease (AD)

Background Current epidemiological studies have examined the associations between moderate and severe traumatic brain injury (TBI) and their risks of developing neurodegenerative diseases. Concussion, also known as mild TBI (mTBI), is however quite distinct from moderate or severe TBIs. Only few studies in this burgeoning area have examined concussion—especially repetitive episodes—and neurodegenerative diseases. Thus, no definite relationship has been established between them.

Objectives This review will discuss the available literatures linking concussion and amyotrophic lateral sclerosis (ALS) and Alzheimer’s disease (AD).

Materials and Methods Given the complexity of this subject, a realist review methodology was selected which includes clarifying the scope and developing a theoretical framework, developing a search strategy, selection and appraisal, data extraction, and synthesis. A detailed literature matrix was set out in order to get relevant and recent findings on this topic.

Results Presently, there is no objective clinical test for the diagnosis of concussion because the features are less obvious on physical examination. Absence of an objective test in diagnosing concussion sometimes leads to skepticism when confirming the presence or absence of concussion. Intriguingly, several possible explanations have been proposed in the pathological mechanisms that lead to the development of some neurodegenerative disorders (such as ALS and AD) and concussion but the two major events are deposition of tau proteins (abnormal microtubule proteins) and neuroinflammation, which ranges from glutamate excitotoxicity pathways and inflammatory pathways (which leads to a rise in the metabolic demands of microglia cells and neurons), to mitochondrial function via the oxidative pathways.

Conclusion mTBI constitutes majority of brain injuries. However, studies have focused mostly on moderate-to-severe TBI as highlighted above with inconclusive and paucity of studies linking concussion and neurodegenerative disorders. Although, it is highly probable that repetitive concussion (mTBI) and subconcussive head injuries may be risk factors for ALS) and AD from this review. It will be imperative therefore to conduct more research with a focus on mTBI and its association with ALS and AD.

Improving mitochondria and ER stability helps eliminate upper motor neuron degeneration that occurs due to mSOD1 toxicity and TDP-43 pathology

BACKGROUND

Upper motor neurons (UMNs) are a key component of motor neuron circuitry. Their degeneration is a hallmark for diseases, such as hereditary spastic paraplegia (HSP), primary lateral sclerosis (PLS), and amyotrophic lateral sclerosis (ALS). Currently there are no preclinical assays investigating cellular responses of UMNs to compound treatment, even for diseases of the UMNs. The basis of UMN vulnerability is not fully understood, and no compound has yet been identified to improve the health of diseased UMNs: two major roadblocks for building effective treatment strategies.

METHODS

Novel UMN reporter models, in which UMNs that are diseased because of misfolded superoxide dismutase protein (mSOD1) toxicity and TDP-43 pathology are labeled with eGFP expression, allow direct assessment of UMN response to compound treatment. Electron microscopy reveals very precise aspects of endoplasmic reticulum (ER) and mitochondrial damage. Administration of NU-9, a compound initially identified based on its ability to reduce mSOD1 toxicity, has profound impact on improving the health and stability of UMNs, as identified by detailed cellular and ultrastructural analyses.

RESULTS

Problems with mitochondria and ER are conserved in diseased UMNs among different species. NU-9 has drug-like pharmacokinetic properties. It lacks toxicity and crosses the blood brain barrier. NU-9 improves the structural integrity of mitochondria and ER, reduces levels of mSOD1, stabilizes degenerating UMN apical dendrites, improves motor behavior measured by the hanging wire test, and eliminates ongoing degeneration of UMNs that become diseased both because of mSOD1 toxicity and TDP-43 pathology, two distinct and important overarching causes of motor neuron degeneration.

CONCLUSIONS

Mechanism-focused and cell-based drug discovery approaches not only addressed key cellular defects responsible for UMN loss, but also identified NU-9, the first compound to improve the health of diseased UMNs, neurons that degenerate in ALS, HSP, PLS, and ALS/FTLD patients.

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.

The role of TDP-43 propagation in neurodegenerative diseases: integrating insights from clinical and experimental studies

TAR DNA-binding protein 43 (TDP-43) is a highly conserved nuclear RNA/DNA-binding protein involved in the regulation of RNA processing. The accumulation of TDP-43 aggregates in the central nervous system is a common feature of many neurodegenerative diseases, such as amyotrophic lateral sclerosis (ALS), frontotemporal dementia (FTD), Alzheimer's disease (AD), and limbic predominant age-related TDP-43 encephalopathy (LATE). Accumulating evidence suggests that prion-like spreading of aberrant protein aggregates composed of tau, amyloid-β, and α-synuclein is involved in the progression of neurodegenerative diseases such as AD and PD. Similar to those of prion-like proteins, pathological aggregates of TDP-43 can be transferred from cell-to-cell in a seed-dependent and self-templating manner. Here, we review clinical and experimental studies supporting the prion-like spreading of misfolded TDP-43 and discuss the molecular mechanisms underlying the propagation of these pathological aggregated proteins. The idea that misfolded TDP-43 spreads in a prion-like manner between cells may guide novel therapeutic strategies for TDP-43-associated neurodegenerative diseases.

Why TDP-43? Why Not? Mechanisms of Metabolic Dysfunction in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a rapidly progressive and fatal neurodegenerative disorder for which there is no effective curative treatment available and minimal palliative care. Mutations in the gene encoding the TAR DNA-binding protein 43 (TDP-43) are a well-recognized genetic cause of ALS, and an imbalance in energy homeostasis correlates closely to disease susceptibility and progression. Considering previous research supporting a plethora of downstream cellular impairments originating in the histopathological signature of TDP-43, and the solid evidence around metabolic dysfunction in ALS, a causal association between TDP-43 pathology and metabolic dysfunction cannot be ruled out. Here we discuss how TDP-43 contributes on a molecular level to these impairments in energy homeostasis, and whether the protein's pathological effects on cellular metabolism differ from those of other genetic risk factors associated with ALS such as superoxide dismutase 1 (SOD1), chromosome 9 open reading frame 72 (C9orf72) and fused in sarcoma (FUS).

Cortical microstructure in the amyotrophic lateral sclerosis-frontotemporal dementia continuum

OBJECTIVE

To characterize the cortical macrostructure and microstructure of behavioral and cognitive changes along the amyotrophic lateral sclerosis (ALS)-frontotemporal dementia (FTD) continuum.

METHODS

We prospectively recruited 88 participants with a 3T MRI structural and diffusion-weighted imaging sequences: 31 with ALS, 20 with the behavioral variant of FTD (bvFTD), and 37 cognitively normal controls. Participants with ALS underwent a comprehensive cognitive and behavioral assessment and were dichotomized into ALS without cognitive or behavioral impairment (ALSno-cbi; n = 12) and ALS with cognitive or behavioral impairment (ALScbi; n = 19). We computed cortical thickness and cortical mean diffusivity using a surface-based approach and explored the cortical correlates of cognitive impairment with the Edinburgh Cognitive and Behavioral ALS Screen.

RESULTS

The ALSno-cbi and ALScbi groups showed different patterns of reduced cortical thickness and increased cortical mean diffusivity. In the ALSno-cbi group, cortical thinning was restricted mainly to the dorsal motor cortex. In contrast, in the ALScbi group, cortical thinning was observed primarily on frontoinsular and temporal regions bilaterally. There were progressive cortical mean diffusivity changes along the ALSno-cbi, ALScbi, and bvFTD clinical continuum. Participants with ALS with either cognitive or behavioral impairment showed increased cortical mean diffusivity in the prefrontal cortex in the absence of cortical thickness.

CONCLUSIONS

Cortical mean diffusivity might be a useful biomarker for the study of extramotor cortical neurodegeneration in the ALS-FTD clinical spectrum.

CLASSIFICATION OF EVIDENCE

This study provides Class III evidence that the cortical microstructure correlates with cognitive impairment in the ALS-FTD continuum.

Neuropathological profile of long-duration amyotrophic lateral sclerosis in military Veterans

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder affecting both the upper and lower motor neurons. Although ALS typically leads to death within 3 to 5 years after initial symptom onset, approximately 10% of patients with ALS live more than 10 years after symptom onset. We set out to determine similarities and differences in clinical presentation and neuropathology in persons with ALS with long vs. those with standard duration. Participants were United States military Veterans with a pathologically confirmed diagnosis of ALS (n = 179), dichotomized into standard duration (<10 years) and long-duration (≥10 years). The ALS Functional Rating Scale-Revised (ALSFRS-R) was administered at study entry and semi-annually thereafter until death. Microglial density was determined in a subset of participants. long-duration ALS occurred in 76 participants (42%) with a mean disease duration of 16.3 years (min/max = 10.1/42.2). Participants with long-duration ALS were younger at disease onset (P = 0.002), had a slower initial ALS symptom progression on the ALSFRS-R (P < 0.001) and took longer to diagnose (P < 0.002) than standard duration ALS. Pathologically, long-duration ALS was associated with less frequent TDP-43 pathology (P < 0.001). Upper motor neuron degeneration was similar; however, long-duration ALS participants had less severe lower motor neuron degeneration at death (P < 0.001). In addition, the density of microglia was decreased in the corticospinal tract (P = 0.017) and spinal cord anterior horn (P = 0.009) in long-duration ALS. Notably, many neuropathological markers of ALS were similar between the standard and long-duration groups and there was no difference in the frequency of known ALS genetic mutations. These findings suggest that the lower motor neuron system is relatively spared in long-duration ALS and that pathological progression is likely slowed by as yet unknown genetic and environmental modifiers.

Non-invasive characterization of amyotrophic lateral sclerosis in a hTDP-43A315T mouse model: A PET-MR study

Currently TAR DNA binding protein 43 (TDP-43) pathology, underlying Amyotrophic Lateral Sclerosis (ALS), remains poorly understood which hinders both clinical diagnosis and drug discovery efforts. To better comprehend the disease pathophysiology, positron emission tomography (PET) and multi-parametric magnetic resonance imaging (mp-MRI) provide a non-invasive mode to investigate molecular, structural, and neurochemical abnormalities in vivo. For the first time, we report the findings of a longitudinal PET-MR study in the TDP-43^A315T ALS mouse model, investigating disease-related changes in the mouse brain. 2-deoxy-2-[¹⁸F]fluoro-D-glucose [¹⁸F]FDG PET showed significantly lowered glucose metabolism in the motor and somatosensory cortices of TDP-43^A315T mice whereas metabolism was elevated in the region covering the bilateral substantia nigra, reticular and amygdaloid nucleus between 3 and 7 months of age, as compared to non-transgenic controls. MR spectroscopy data showed significant changes in glutamate + glutamine (Glx) and choline levels in the motor cortex and hindbrain of TDP-43^A315T mice compared to controls. Cerebral blood flow (CBF) measurements, using an arterial spin labelling approach, showed no significant age- or group-dependent changes in brain perfusion. Diffusion MRI indices demonstrated transient changes in different motor areas of the brain in TDP-43^A315T mice around 14 months of age. Cytoplasmic TDP-43 proteinaceous inclusions were observed in the brains of symptomatic, 18-month-old mice, but not in non-symptomatic transgenic or wild-type mice. Our results reveal that disease- and age-related functional and neurochemical alterations, together with limited structural changes, occur in specific brain regions of transgenic TDP-43^A315T mice, as compared to their healthy counterparts. Altogether these findings shed new light on TDP-43^A315T disease pathogenesis and may prove useful for clinical management of ALS.

Executive, language and fluency dysfunction are markers of localised TDP-43 cerebral pathology in non-demented ALS

OBJECTIVE

Approximately 35% of patients with amyotrophic lateral sclerosis (ALS) exhibit mild cognitive deficits in executive functions, language and fluency, without dementia. The precise pathology of these extramotor symptoms has remained unknown. This study aimed to determine the pathological correlate of cognitive impairment in patients with non-demented ALS.

METHODS

In-depth neuropathological analysis of 27 patients with non-demented ALS who had undergone cognitive testing (Edinburgh Cognitive and Behaviour ALS Screen (ECAS)) during life. Analysis involved assessing 43 kDa Tar-DNA binding protein (TDP-43) accumulation in brain regions specifically involved in executive functions, language functions and verbal fluency to ascertain whether functional deficits would relate to a specific regional distribution of pathology.

RESULTS

All patients with cognitive impairment had TDP-43 pathology in extramotor brain regions (positive predictive value of 100%). The ECAS also predicted TDP-43 pathology with 100% specificity in brain regions associated with executive, language and fluency domains. We also detected a subgroup with no cognitive dysfunction, despite having substantial TDP-43 pathology, so called mismatch cases.

CONCLUSIONS

Cognitive impairment as detected by the ECAS is a valid predictor of TDP-43 pathology in non-demented ALS. The profile of mild cognitive deficits specifically predicts regional cerebral involvement. These findings highlight the utility of the ECAS in accurately assessing the pathological burden of disease.

Improved detection of RNA foci in C9orf72 amyotrophic lateral sclerosis post-mortem tissue using BaseScope™ shows a lack of association with cognitive dysfunction

The C9orf72 hexanucleotide repeat expansion is the commonest known genetic mutation in amyotrophic lateral sclerosis. A neuropathological hallmark is the intracellular accumulation of RNA foci. The role that RNA foci play in the pathogenesis of amyotrophic lateral sclerosis is widely debated. Historically, C9orf72 RNA foci have been identified using in situ hybridization. Here, we have implemented BaseScope™, a high-resolution modified in situ hybridization technique. We demonstrate that previous studies have underestimated the abundance of RNA foci in neurons and glia. This improved detection allowed us to investigate the abundance, regional distribution and cell type specificity of sense C9orf72 RNA foci in post-mortem brain and spinal cord tissue of six deeply clinically phenotyped C9orf72 patients and six age- and sex-matched controls. We find a correlation between RNA foci and the accumulation of transactive response DNA-binding protein of 43 kDa in spinal motor neurons (r_s = 0.93; P = 0.008), but not in glia or cortical motor neurons. We also demonstrate that there is no correlation between the presence of RNA foci and the accumulation of transactive response DNA binding protein of 43 kDa in extra-motor brain regions. Furthermore, there is no association between the presence of RNA foci and cognitive indices. These results highlight the utility of BaseScope™ in the clinicopathological assessment of the role of sense RNA foci in C9orf72.

Application of CRISPR genetic screens to investigate neurological diseases

The adoption of CRISPR-Cas9 technology for functional genetic screens has been a transformative advance. Due to its modular nature, this technology can be customized to address a myriad of questions. To date, pooled, genome-scale studies have uncovered genes responsible for survival, proliferation, drug resistance, viral susceptibility, and many other functions. The technology has even been applied to the functional interrogation of the non-coding genome. However, applications of this technology to neurological diseases remain scarce. This shortfall motivated the assembly of a review that will hopefully help researchers moving in this direction find their footing. The emphasis here will be on design considerations and concepts underlying this methodology. We will highlight groundbreaking studies in the CRISPR-Cas9 functional genetics field and discuss strengths and limitations of this technology for neurological disease applications. Finally, we will provide practical guidance on navigating the many choices that need to be made when implementing a CRISPR-Cas9 functional genetic screen for the study of neurological diseases.

Mitoautophagy: A Unique Self-Destructive Path Mitochondria of Upper Motor Neurons With TDP-43 Pathology Take, Very Early in ALS

Mitochondrial dysfunction is one of the converging paths for many neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS), and TDP-43 pathology is the most common proteinopathy detected in ALS and ALS/Frontotemporal lobar degeneration (ALS/FTLD). We recently identified mitochondrial problems in corticospinal motor neurons (CSMN) and in Betz cells of patients with TDP-43 pathology. However, the timing and the extent of mitochondrial defects, and their mode of degeneration have not been revealed. Because it is important to reveal when problems first begin to emerge and whether they are shared or unique, we investigated the health and integrity of mitochondria in CSMN of prpTDP-43^A315T, PFN1^G118V, and hSOD1^G93A mice at P15 (post-natal day 15)—a very early age in mice without any sign of cellular degeneration.Utilization of immuno-coupled electron microscopy for a detailed surveillance of mitochondria in CSMN and other non-CSMN cells revealed presence of a novel self-destructive path of mitochondrial degeneration, which we named mitoautophagy. Mitoauthopgy is different from mitophagy, as it does not require autophagosome-mediated degradation. In contrast, in this novel path, mitochondria can clear themselves independently. We find that even at this early age, all diseased CSMN begin to display mitochondrial defects, whereas mitochondria in non-CSMN cells are healthy. Our findings not only reveal mitoautophagy as a novel path of mitochondrial clearance that occurs prior to neuronal vulnerability, but it also highlights that it is present mainly in the upper motor neurons of prpTDP-43^A315T and PFN1^G118V mice, which mimic many aspects of the disease in patients with TDP-43 pathology.

MCP1-CCR2 and neuroinflammation in the ALS motor cortex with TDP-43 pathology

BACKGROUND

The involvement of non-neuronal cells and the cells of innate immunity has been attributed to the initiation and progression of ALS. TDP-43 pathology is observed in a broad spectrum of ALS cases and is one of the most commonly shared pathologies. The potential involvement of the neuroimmune axis in the motor cortex of ALS patients with TDP-43 pathology needs to be revealed. This information is vital for building effective treatment strategies.

METHODS

We investigated the presence of astrogliosis and microgliosis in the motor cortex of ALS patients with TDP-43 pathology. prpTDP-43^A315T-UeGFP mice, corticospinal motor neuron (CSMN) reporter line with TDP-43 pathology, are utilized to reveal the timing and extent of neuroimmune interactions and the involvement of non-neuronal cells to neurodegeneration. Electron microscopy and immunolabeling techniques are used to mark and monitor cells of interest.

RESULTS

We detected both activated astrocytes and microglia, especially rod-like microglia, in the motor cortex of patients and TDP-43 mouse model. Besides, CCR2+ TMEM119- infiltrating monocytes were detected as they penetrate the brain parenchyma. Interestingly, Betz cells, which normally do not express MCP1, were marked with high levels of MCP1 expression when diseased.

CONCLUSIONS

There is an early contribution of a neuroinflammatory response for upper motor neuron (UMN) degeneration with respect to TDP-43 pathology, and MCP1-CCR2 signaling is important for the recognition of diseased upper motor neurons by infiltrating monocytes. The findings are conserved among species and are observed in both ALS and ALS-FTLD patients.

White matter changes in the perforant path area in patients with amyotrophic lateral sclerosis

OBJECTIVE

The aim of this study was to test the hypothesis that white matter degeneration of the perforant path - as part of the Papez circuit - is a key feature of amyotrophic lateral sclerosis (ALS), even in the absence of frontotemporal dementia (FTD) or deposition of pTDP-43 inclusions in hippocampal granule cells.

METHODS

We used diffusion Magnetic Resonance Imaging (dMRI), polarized light imaging (PLI) and immunohistochemical analysis of post mortem hippocampus specimens from controls (n = 5) and ALS patients (n = 14) to study white matter degeneration in the perforant path.

RESULTS

diffusion Magnetic Resonance Imaging demonstrated a decrease in fractional anisotropy (P = 0.01) and an increase in mean diffusivity (P = 0.01) in the perforant path in ALS compared to controls. PLI-myelin density was lower in ALS (P = 0.05) and correlated with fractional anisotropy (r = 0.52, P = 0.03). These results were confirmed by immunohistochemistry; both myelin (proteolipid protein, P = 0.03) and neurofilaments (SMI-312, P = 0.02) were lower in ALS. Two out of the fourteen ALS cases showed pTDP-43 pathology in the dentate gyrus, but with comparable myelination levels in the perforant path to other ALS cases.

CONCLUSION

We conclude that degeneration of the perforant path occurs in ALS patients and that this may occur before, or independent of, pTDP-43 aggregation in the dentate gyrus of the hippocampus. Future research should focus on correlating the degree of cognitive decline to the amount of white matter atrophy in the perforant path.

Mitochondria, ER, and nuclear membrane defects reveal early mechanisms for upper motor neuron vulnerability with respect to TDP-43 pathology

Insoluble aggregates containing TDP-43 are widely observed in the diseased brain, and defined as "TDP-43 pathology" in a spectrum of neurodegenerative diseases, such as amyotrophic lateral sclerosis (ALS), Alzheimer's disease and ALS with frontotemporal dementia. Here we report that Betz cells of patients with TDP-43 pathology display a distinct set of intracellular defects especially at the site of nuclear membrane, mitochondria and endoplasmic reticulum (ER). Numerous TDP-43 mouse models have been generated to discern the cellular and molecular basis of the disease, but mechanisms of neuronal vulnerability remain unknown. In an effort to define the underlying causes of corticospinal motor neuron (CSMN) degeneration, we generated and characterized a novel CSMN reporter line with TDP-43 pathology, the prp-TDP-43^A315T-UeGFP mice. We find that TDP-43 pathology related intracellular problems emerge very early in the disease. The Betz cells in humans and CSMN in mice both have impaired mitochondria, and display nuclear membrane and ER defects with respect to TDP-43 pathology.

Rapidly progressive amyotrophic lateral sclerosis is associated with microglial reactivity and small heat shock protein expression in reactive astrocytes

AIMS

Amyotrophic lateral sclerosis (ALS) is a chronic neurodegenerative disease characterized by progressive loss of motor neurons, muscle weakness, spasticity, paralysis and death usually within 2-5 years of onset. Neuroinflammation is a hallmark of ALS pathology characterized by activation of glial cells, which respond by upregulating small heat shock proteins (HSPBs), but the exact underlying pathological mechanisms are still largely unknown. Here, we investigated the association between ALS disease duration, lower motor neuron loss, TARDNA-binding protein 43 (TDP-43) pathology, neuroinflammation and HSPB expression.

METHODS

With immunohistochemistry, we examined HSPB1, HSPB5, HSPB6, HSPB8 and HSP16.2 expression in cervical, thoracic and sacral spinal cord regions in 12 ALS cases, seven with short disease duration (SDD), five with moderate disease duration (MDD), and ten age-matched controls. Expression was quantified using ImageJ to examine HSP expression, motor neuron numbers, microglial and astrocyte density and phosphorylated TDP-43 (pTDP-43+) inclusions.

RESULTS

SDD was associated with elevated HSPB5 and 8 expression in lateral tract astrocytes, while HSP16.2 expression was increased in astrocytes in MDD cases. SDD cases had higher numbers of motor neurons and microglial activation than MDD cases, but similar levels of motor neurons with pTDP-43+ inclusions.

CONCLUSIONS

Increased expression of several HSPBs in lateral column astrocytes suggests that astrocytes play a role in the pathogenesis of ALS. SDD is associated with increased microgliosis, HSPB5 and 8 expression in astrocytes, and only minor changes in motor neuron loss. This suggests that the interaction between motor neurons, microglia and astrocytes determines neuronal fate and functional decline in ALS.

Phosphorylated TDP-43 Staging of Primary Age-Related Tauopathy

Primary age-related tauopathy (PART) is characterized by tau neurofibrillary tangles (NFTs) in the absence of amyloid plaque pathology. In the present study, we analyzed the distribution patterns of phosphorylated 43-kDa TAR DNA-binding protein (pTDP-43) in the brains of patients with PART. Immunohistochemistry and immunofluorescence double-labeling in multiple brain regions was performed on brain tissues from PART, Alzheimer's disease (AD), and aging control cases. We examined the regional distribution patterns of pTDP-43 intraneuronal inclusions in PART with Braak NFT stages > 0 and ≤ IV, and a Thal phase of 0 (no beta-amyloid present). We found four stages which indicated potentially sequential dissemination of pTDP-43 in PART. Stage I was characterized by the presence of pTDP-43 lesions in the amygdala, stage II by such lesions in the hippocampus, stage III by spread of pTDP-43 to the neocortex, and stage IV by pTDP-43 lesions in the putamen, pallidum, and insular cortex. In general, the distribution pattern of pTDP-43 pathology in PART cases was similar to the early TDP-43 stages reported in AD, but tended to be more restricted to the limbic system. However, there were some differences in the distribution patterns of pTDP-43 between PART and AD, especially in the dentate gyrus of the hippocampus. Positive correlations were found in PART between the Braak NFT stage and the pTDP-43 stage and density.

Revisiting the concept of amyotrophic lateral sclerosis as a multisystems disorder of limited phenotypic expression

PURPOSE OF REVIEW

The current review will examine the contemporary evidence that amyotrophic lateral sclerosis (ALS) is a syndrome in which the unifying feature is a progressive loss of upper and lower motor neuron function.

RECENT FINDINGS

Although ALS is traditionally viewed as a neurodegenerative disorder affecting the motor neurons, there is considerable phenotypic heterogeneity and widespread involvement of the central nervous system. A broad range of both causative and disease modifying genetic variants are associated with both sporadic and familial forms of ALS. A significant proportion of ALS patients have an associated frontotemporal dysfunction which can be a harbinger of a significantly shorter survival and for which there is increasing evidence of a fundamental disruption of tau metabolism in those affected individuals. Although the traditional neuropathology of the degenerating motor neurons in ALS is that of neuronal cytoplasmic inclusions composed neuronal intermediate filaments, the presence of neuronal cytoplasmic inclusions composed of RNA binding proteins suggests a key role for RNA dysmetabolism in the pathogenesis of ALS.

SUMMARY

ALS is a complex multisystem neurodegenerative syndrome with marked heterogeneity at not only the level of clinical expression, but also etiologically.

CK2 Phosphorylating I2PP2A/SET Mediates Tau Pathology and Cognitive Impairment

Casein kinase 2 (CK2) is highly activated in Alzheimer disease (AD) and is associated with neurofibrillary tangles formation. Phosphorylated SET, a potent PP2A inhibitor, mediates tau hyperphosphorylation in AD. However, whether CK2 phosphorylates SET and regulates tau pathological phosphorylation in AD remains unclear. Here, we show that CK2 phosphorylating SET at Ser9 induced tau hyperphosphorylation in AD. We found that either Aβ treatment or tau overexpression stimulated CK2 activation leading to SET Ser9 hyperphosphorylation in neurons and animal models, while inhibition of CK2 by TBB abolished this event. Overexpression of CK2 in mouse hippocampus via virus injection induced cognitive deficit associated with SET Ser9 hyperphosphorylation. Injection of SET Ser9 phosphorylation mimetic mutant induced tau pathology and behavior impairments. Conversely co-injection of non-phosphorylated SET S9A with CK2 abolished the CK2 overexpression-induced AD pathology and cognitive deficit. Together, our data demonstrate that CK2 phosphorylates SET at Ser9 leading to SET cytoplasmic translocation and inhibition of PP2A resulting in tau pathology and cognitive impairments.

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.

Phosphorylated TDP-43 (pTDP-43) aggregates in the axial skeletal muscle of patients with sporadic and familial amyotrophic lateral sclerosis

Muscle atrophy with weakness is a core feature of amyotrophic lateral sclerosis (ALS) that has long been attributed to motor neuron loss alone. However, several studies in ALS patients, and more so in animal models, have challenged this assumption with the latter providing direct evidence that muscle can play an active role in the disease. Here, we examined the possible role of cell autonomous pathology in 148 skeletal muscle samples from 57 ALS patients, identifying phosphorylated TAR DNA-binding protein (pTDP-43) inclusions in the muscle fibers of 19 patients (33.3%) and 24 tissue samples (16.2% of specimens). A muscle group-specific difference was identified with pTDP-43 pathology being significantly more common in axial (paraspinous, diaphragm) than appendicular muscles (P = 0.0087). This pathology was not significantly associated with pertinent clinical, genetic (c9ALS) or nervous system pathologic data, suggesting it is not limited to any particular subgroup of ALS patients. Among 25 non-ALS muscle samples, pTDP-43 inclusions were seen only in the autophagy-related disorder inclusion body myositis (IBM) (n = 4), where they were more diffuse than in positive ALS samples (P = 0.007). As in IBM samples, pTDP-43 aggregates in ALS were p62/ sequestosome-1-positive, potentially indicating induction of autophagy. Phospho-TDP-43-positive ALS and IBM samples also showed significant up-regulation of TARDBP and SQSTM1 expression. These findings implicate axial skeletal muscle as an additional site of pTDP-43 pathology in some ALS patients, including sporadic and familial cases, which is deserving of further investigation.

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.

Regulation of HSF1 protein stabilization: An updated review

Heat shock factor 1 (HSF1) is a transcriptional factor that determines the efficiency of heat shock responses (HSRs) in the cell. Given its function has been extensively studied in recent years, HSF1 is considered a potential target for the treatment of disorders associated with protein aggregation. The activity of HSF1 is traditionally regulated at the transcriptional level in which the transactivation domain of HSF1 is modified by extensive array of pos-translational modifications, such as phosphorylation, sumoylation, and acetylation. Recently, HSF1 is also reported to be regulated at the monomeric level. For example, in neurodegenerative disorders such as Huntington's disease and Alzheimer's disease the expression levels of the monomeric HSF1 are found to be reduced markedly. Methylene blue (MB) and riluzole, two clinical available drugs, increase the amount of the monomeric HSF1 in both cells and animals. Since the monomeric HSF1 not only determines the efficiency of HSRs, but exerts protective effects in a trimerization-independent manner, increasing the amount of the monomeric HSF1 via stabilization of HSF1 may be an alternative strategy for the amplification of HSR. However, to date we have no outlined knowledges about HSF1 protein stabilization, though studies regarding the regulation of the monomeric HSF1 have been documented in recent years. Here, we summarize the regulation of the monomeric HSF1 by some previously reported factors, such as synuclein, Huntingtin (Htt), TDP-43, unfolded protein response (UPR), MB and doxorubicin (DOX), as well as their possible mechanisms, aiming to push the understanding about HSF1 protein stabilization.

Amyotrophic lateral sclerosis modifies progenitor neural proliferation in adult classic neurogenic brain niches

BACKGROUND

Adult neurogenesis persists through life at least in classic neurogenic niches. Neurogenesis has been previously described as reduced in neurodegenerative diseases. There is not much knowledge about is adult neurogenesis is or not modified in amyotrophy lateral sclerosis (ALS). All previous publications has studied the ALS SOD1 (superoxide dismutase) transgenic mouse model. The purpose of this study is to examine the process of adult neurogenesis in classic niches (subventricular zone [SVZ] and subgranular zone [SGZ] of the dentate gyrus) in patients with amyotrophic lateral sclerosis (ALS), both with (ALS-FTD) and without associated frontotemporal dementia (FTD).

METHODS

We studied 9 autopsies of patients with ALS (including 2 with ALS-FTD) and 4 controls. ALS was confirmed histologically. Studies of the SVZ and SGZ were conducted using markers of proliferation (Ki-67, PCNA), of pluripotent neural progenitor cells (GFAPδ), neuroblasts (PSA-NCAM, DCX, TUJ1), and an astrocyte marker (GFAP). Results were analyzed with non-parametric tests. We then studied correlations between the different markers and the percentage of phosphorylated TDP-43 (pTDP-43).

RESULTS

We observed a statistically significant increase in proliferation in the SVZ in all patients with ALS. While this increase was more marked in ALS forms associated with dementia, the small sample size does not permit a statistical subgroup analysis. In contrast, proliferation in the SGZ was decreased in all patients. These alterations showed a positive and direct correlation with the percentage of pTDP-43 in the SVZ, and a negative, exponential correlation with that percentage in the SGZ.

CONCLUSIONS

We observed alterations of the proliferation of neural progenitor in classic adult neurogenic niches in patients with ALS. The 2 neurogenic niches exhibited opposite changes such that proliferation increased in the SVZ and decreased in the SGZ.