The frontotemporal dementia-motor neuron disease continuum

UNC13A Polymorphism Influences Survival in Patients with Frontotemporal Dementia

UNC13A (rs12608932-CC) is associated with both amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), and shortens survival in ALS. We aim to describe the association for UNC13A and survival in FTD. We included 626 patients with FTD from Dutch memory clinics, including a subcohort of 150 patients with TDP-43 pathology. Survival analyses were performed using Cox proportional hazard models in a recessive manner. Homozygosity for rs12608932-C in UNC13A was associated with a shorter survival compared with other genotypes (hazard ratio [HR] = 1.28, 95% confidence interval [CI] = 1.02-1.60, p = 0.033), which has implications for patient counselling and trial design. ANN NEUROL 2025;97:1062-1066.

Molecular mechanisms and consequences of TDP-43 phosphorylation in neurodegeneration

Increased phosphorylation of TDP-43 is a pathological hallmark of several neurodegenerative disorders, including amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). However, the regulation and roles of TDP-43 phosphorylation remain incompletely understood. A variety of techniques have been utilized to understand TDP-43 phosphorylation, including kinase/phosphatase manipulation, phosphomimic variants, and genetic, physical, or chemical inducement in a variety of cell cultures and animal models, and via analyses of post-mortem human tissues. These studies have produced conflicting results: suggesting incongruously that TDP-43 phosphorylation may either drive disease progression or serve a neuroprotective role. In this review, we explore the roles of regulators of TDP-43 phosphorylation including the putative TDP-43 kinases c-Abl, CDC7, CK1, CK2, IKKβ, p38α/MAPK14, MEK1, TTBK1, and TTBK2, and TDP-43 phosphatases PP1, PP2A, and PP2B, in disease. Building on recent studies, we also examine the consequences of TDP-43 phosphorylation on TDP-43 pathology, especially related to TDP-43 mislocalisation, liquid-liquid phase separation, aggregation, and neurotoxicity. By comparing conflicting findings from various techniques and models, this review highlights both the discrepancies and unresolved aspects in the understanding of TDP-43 phosphorylation. We propose that the role of TDP-43 phosphorylation is site and context dependent, and includes regulation of liquid-liquid phase separation, subcellular mislocalisation, and degradation. We further suggest that greater consideration of the normal functions of the regulators of TDP-43 phosphorylation that may be perturbed in disease is warranted. This synthesis aims to build towards a comprehensive understanding of the complex role of TDP-43 phosphorylation in the pathogenesis of neurodegeneration.

The Regulation of TDP-43 Structure and Phase Transitions: A Review

The transactive response DNA binding protein 43 (TDP-43) is an RNA/DNA-binding protein that is involved in a number of cellular functions, including RNA processing and alternative splicing, RNA transport and translation, and stress granule assembly. It has attracted significant attention for being the primary component of cytoplasmic inclusions in patients with amyotrophic lateral sclerosis or frontotemporal dementia. Mounting evidence suggests that both cytoplasmic aggregation of TDP-43 and loss of nuclear TDP-43 function contribute to TDP-43 pathology. Furthermore, recent studies have demonstrated that TDP-43 is an important component of many constitutive or stress-induced biomolecular condensates. Dysregulation or liquid-to-gel transition of TDP-43 condensates can lead to alterations in TDP-43 function and the formation of TDP-43 amyloid fibrils. In this review, we summarize recent research progress on the structural characterization of TDP-43 and the TDP-43 phase transition. In particular, the roles that disease-associated genetic mutations, post-translational modifications, and extrinsic stressors play in the transitions among TDP-43 monomers, liquid condensates, solid condensates, and fibrils are discussed. Finally, we discuss the effectiveness of available regulators of TDP-43 phase separation and aggregation. Understanding the underlying mechanisms that drive the pathological transformation of TDP-43 could help develop therapeutic strategies for TDP-43 pathology.

A stress-dependent TDP-43 SUMOylation program preserves neuronal function

Amyotrophic Lateral Sclerosis (ALS) and Frontotemporal Dementia (FTD) are overwhelmingly linked to TDP-43 dysfunction. Mutations in TDP-43 are rare, indicating that the progressive accumulation of exogenous factors - such as cellular stressors - converge on TDP-43 to play a key role in disease pathogenesis. Post translational modifications such as SUMOylation play essential roles in response to such exogenous stressors. We therefore set out to understand how SUMOylation may regulate TDP-43 in health and disease. We find that TDP-43 is regulated dynamically via SUMOylation in response to cellular stressors. When this process is blocked in vivo, we note age-dependent TDP-43 pathology and sex-specific behavioral deficits linking TDP-43 SUMOylation with aging and disease. We further find that SUMOylation is correlated with human aging and disease states. Collectively, this work presents TDP-43 SUMOylation as an early physiological response to cellular stress, disruption of which may confer a risk for TDP-43 proteinopathy.

Activating autophagy to eliminate toxic protein aggregates with small molecules in neurodegenerative diseases

Neurodegenerative diseases (NDs), such as Alzheimer disease, Parkinson disease, Huntington disease, amyotrophic lateral sclerosis, and frontotemporal dementia, are well known to pose formidable challenges for their treatment due to their intricate pathogenesis and substantial variability among patients, including differences in environmental exposures and genetic predispositions. One of the defining characteristics of NDs is widely reported to be the buildup of misfolded proteins. For example, Alzheimer disease is marked by amyloid beta and hyperphosphorylated Tau aggregates, whereas Parkinson disease exhibits α-synuclein aggregates. Amyotrophic lateral sclerosis and frontotemporal dementia exhibit TAR DNA-binding protein 43, superoxide dismutase 1, and fused-in sarcoma protein aggregates, and Huntington disease involves mutant huntingtin and polyglutamine aggregates. These misfolded proteins are the key biomarkers of NDs and also serve as potential therapeutic targets, as they can be addressed through autophagy, a process that removes excess cellular inclusions to maintain homeostasis. Various forms of autophagy, including macroautophagy, chaperone-mediated autophagy, and microautophagy, hold a promise in eliminating toxic proteins implicated in NDs. In this review, we focus on elucidating the regulatory connections between autophagy and toxic proteins in NDs, summarizing the cause of the aggregates, exploring their impact on autophagy mechanisms, and discussing how autophagy can regulate toxic protein aggregation. Moreover, we underscore the activation of autophagy as a potential therapeutic strategy across different NDs and small molecules capable of activating autophagy pathways, such as rapamycin targeting the mTOR pathway to clear α-synuclein and Sertraline targeting the AMPK/mTOR/RPS6KB1 pathway to clear Tau, to further illustrate their potential in NDs' therapeutic intervention. Together, these findings would provide new insights into current research trends and propose small-molecule drugs targeting autophagy as promising potential strategies for the future ND therapies. SIGNIFICANCE STATEMENT: This review provides an in-depth overview of the potential of activating autophagy to eliminate toxic protein aggregates in the treatment of neurodegenerative diseases. It also elucidates the fascinating interrelationships between toxic proteins and the process of autophagy of "chasing and escaping" phenomenon. Moreover, the review further discusses the progress utilizing small molecules to activate autophagy to improve the efficacy of therapies for neurodegenerative diseases by removing toxic protein aggregates.

Quantifying neurodegeneration within subdivisions of core motor pathways in amyotrophic lateral sclerosis using diffusion MRI

BACKGROUND

Diffusion MRI is sensitive to white matter changes in amyotrophic lateral sclerosis (ALS). The current study aimed to establish disease profiles across core motor pathways, and their relevance to clinical progression in ALS.

METHODS

Sixty-five participants (ALS = 47; Control = 18) were recruited for the study. White matter integrity of motor, somatosensory, and premotor subdivisions within the corticospinal tract and corpus callosum were quantified by fibre density, fibre-bundle cross-section, structural connectivity, and fractional anisotropy. Analyses focused on identifying diffusion metrics and tract profiles sensitive to ALS pathology, and their association with clinical progression.

RESULTS

Reduced fibre density of the motor subdivision of the corpus callosum (CC) and corticospinal tract (CST) demonstrated best performance in classifying ALS from controls (area-under-curve: CCmotor = 0.81, CSTmotor = 0.76). Significant reductions in fibre density (CCmotor: p < 0.001; CSTmotor: p = 0.016), and structural connectivity (CCmotor: p = 0.008; CSTsomatosensory: p = 0.012) indicated presence of ALS pathology. Reduced fibre density & cross-section significantly correlated with severity of functional impairment (ALSFRS-R; CCmotor: r = 0.52, p = 0.019; CSTmotor: r = 0.59, p = 0.016). The largest effect sizes were generally found for motor and somatosensory subdivisions across both major white matter bundles.

CONCLUSION

Current findings suggest that ALS does not uniformly impact the corticospinal tract and corpus callosum. There is a preferential disease profile of neurodegeneration mainly impacting primary motor fibres. Microstructural white matter abnormality indicated presence of ALS pathology while macrostructural white matter abnormality was associated with severity of functional impairment. Quantification of white matter abnormality in corticospinal tract and callosal subdivisions holds translational potential as an imaging biomarker for neurodegeneration in ALS.

Molecular Biomarkers of Neurodegeneration in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is the most prevalent motor neuron disease. However, definitive diagnosis could be delayed by up to 12 months due to the lack of specific and sensitive biomarkers for ALS. In our study, conducted for the first time on a large cohort of ALS patients (n = 100) within the Russian population, we assessed key biomarkers of neurodegenerative pathology, including β-amyloids (Aβ40 and Aβ42) and tau proteins (Tau-total and Tau-p181), as well as other pathogenetically relevant, promising biomarkers such as FGF-21, Kallikrein-6 (KLK-6), NCAM-1, Neurogranin (NRGN), TDP-43, Apolipoprotein E4, Clusterin (Apo J), Complement Factor H, Fetuin-A, α2-Macroglobulin, Apo AI, Apo CIII, Apo E, Complement C3, GDNF, sRAGE, and S100B protein. Significant differences between the ALS patients and the control group were observed for Aβ40 (p = 0.044), Aβ42 (p < 0.001), FGF-21 (p < 0.001), Tau-total (p = 0.001), Tau-p181 (p = 0.014), Clusterin (p < 0.001), Complement C3 (p = 0.001), and S100B (p = 0.024). A significant direct correlation was found between the ALSFRS-R score and concentrations of Aβ40 and Aβ42. Changes in the complement system (Complement C3 and Complement Factor H) were identified, highlighting critical role of neuroinflammatory processes in ALS pathogenesis. Additionally, increased levels of FGF-21 were observed in the patients with the bulbar onset of ALS. Significant increase in the concentration of the chaperone protein clusterin in the patients with rapid disease progression suggests its potential as a prognostic biomarker for motor neuron disease. Furthermore, its role in maintaining proteostasis could provide novel therapeutic targets.

Bioengineered exosomes: Cellular membrane-camouflaged biomimetic nanocarriers for Parkinson's disease management

Parkinson's disease is a prevalent neurological condition that affects around 1% of adults over 60 worldwide. Deep brain stimulation and dopamine replacement therapy are common therapies for Parkinson's disease, yet they are unable to reverse the disease it simply because of the blood brain barrier. The use of bioengineered exosomes to treat Parkinson's disease is being studied because they have the ability to cross the blood-brain barrier. Their natural ability to cross the blood-brain barrier (BBB) and their biocompatibility make them highly suitable for delivering therapeutic agents to manage PD, specifically the role of astrocytes, microglial cells, and alpha-synuclein. It also explores the biogenesis and preparation of these bioengineered exosomes. In comparison to conventional nanocarriers, the modified exosomal-membrane-camouflaged abiotic nanocarriers show improved resilience and compatibility. Improved cellular absorption and targeted delivery of therapeutic payloads, such as medications and enzymes, are being shown in laboratory trials. A viable strategy for treating PD involves combining abiotic nanocarriers with bioengineered exosomal membranes. Despite their promising potential, successful clinical application requires overcoming hurdles related to scalable production, regulatory approval, and long-term safety evaluation. Nevertheless, the innovative use of bioengineered exosomes holds significant promise for advancing PD management and improving patient outcomes through more targeted and effective therapeutic strategies.

Dual-targeting CRISPR-CasRx reduces C9orf72 ALS/FTD sense and antisense repeat RNAs in vitro and in vivo

The most common genetic cause of frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) is an intronic G4C2 repeat expansion in C9orf72. The repeats undergo bidirectional transcription to produce sense and antisense repeat RNA species, which are translated into dipeptide repeat proteins (DPRs). As toxicity has been associated with both sense and antisense repeat-derived RNA and DPRs, targeting both strands may provide the most effective therapeutic strategy. CRISPR-Cas13 systems mature their own guide arrays, allowing targeting of multiple RNA species from a single construct. We show CRISPR-Cas13d variant CasRx effectively reduces overexpressed C9orf72 sense and antisense repeat transcripts and DPRs in HEK cells. In C9orf72 patient-derived iPSC-neuron lines, CRISPR-CasRx reduces endogenous sense and antisense repeat RNAs and DPRs and protects against glutamate-induced excitotoxicity. AAV delivery of CRISPR-CasRx to two distinct C9orf72 repeat mouse models significantly reduced both sense and antisense repeat-containing transcripts. This highlights the potential of RNA-targeting CRISPR systems as therapeutics for C9orf72 ALS/FTD.

Brain neurovascular coupling in amyotrophic lateral sclerosis: Correlations with disease progression and cognitive impairment

BACKGROUND AND PURPOSE

'Neurovascular coupling' (NVC) alterations, assessing the interplay between local cerebral perfusion and neural activity within a given brain region or network, may reflect neurovascular unit impairment in amyotrophic lateral sclerosis (ALS). The aim was to explore NVC as a correlation between the functional connectivity and cerebral blood flow within the large-scale resting-state functional magnetic resonance imaging brain networks in a sample of ALS patients compared to healthy controls (HCs).

METHODS

Forty-eight ALS patients (30 males; mean age 60.64 ± 9.62 years) and 32 HC subjects (14 males; mean age 55.06 ± 16 years) were enrolled and underwent 3 T magnetic resonance imaging. ALS patients were screened by clinical and neuropsychological scales and were retrospectively classified as very fast progressors (VFPs), fast progressors and slow progressors (SPs).

RESULTS

Neurovascular coupling reduction within the default mode network (DMN) (p = 0.005) was revealed in ALS patients compared to HCs, observing, for this network, significant NVC differences between VFP and SP groups. Receiver operating characteristic curve analysis showed that impaired NVC in the DMN at baseline best discriminated VFPs and SPs (area under the curve 75%). Significant correlations were found between NVC and the executive (r = 0.40, p = 0.01), memory (r = 0.32, p = 0.04), visuospatial ability (r = 0.40, p = 0.01) and non-ALS-specific (r = 0.40, p = 0.01) subscores of the Edinburgh Cognitive and Behavioural ALS Screen.

CONCLUSIONS

The reduction of brain NVC in the DMN may reflect largely distributed abnormalities of the neurovascular unit. NVC alterations in the DMN could play a role in anticipating a faster clinical progression in ALS patients, aiding patient selection and monitoring during clinical trials.

C9orf72-Associated Dipeptide Repeat Expansions Perturb ER-Golgi Vesicular Trafficking, Inducing Golgi Fragmentation and ER Stress, in ALS/FTD

Hexanucleotide repeat expansions (HREs) in the chromosome 9 open reading frame 72 (C9orf72) gene are the most frequent genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Both are debilitating neurodegenerative conditions affecting either motor neurons (ALS) in the brain and spinal cord or neurons in the frontal and/or temporal cortical lobes (FTD). HREs undergo repeat-associated non-ATG (RAN) translation on both sense and anti-sense strands, generating five distinct dipeptide repeat proteins (DPRs), poly-GA, -GR, -GP, -PA and -PR. Perturbed proteostasis is well-recognised in ALS pathogenesis, including processes affecting the endoplasmic reticulum (ER) and Golgi compartments. However, these mechanisms have not been well characterised for C9orf72-mediated ALS/FTD. In this study we demonstrate that C9orf72 DPRs polyGA, polyGR and polyGP (× 40 repeats) disrupt secretory protein transport from the ER to the Golgi apparatus in neuronal cells. Consistent with this finding, these DPRs also induce fragmentation of the Golgi apparatus, activate ER stress, and inhibit the formation of the omegasome, the precursor of the autophagosome that originates from ER membranes. We also demonstrate Golgi fragmentation in cells undergoing RAN translation that express polyGP. Furthermore, dysregulated ER-Golgi transport was confirmed in C9orf72 patient dermal fibroblasts. Evidence of aberrant ER-derived vesicles in spinal cord motor neurons from C9orf72 ALS patients compared to controls was also obtained. These data thus confirm that ER proteostasis and ER-Golgi transport is perturbed in C9orf72-ALS in the absence of protein over-expression. Hence this study identifies novel molecular mechanisms associated with the ER and Golgi compartments induced by the C9orf72 HRE.

Membraneless organelles in health and disease: exploring the molecular basis, physiological roles and pathological implications

Once considered unconventional cellular structures, membraneless organelles (MLOs), cellular substructures involved in biological processes or pathways under physiological conditions, have emerged as central players in cellular dynamics and function. MLOs can be formed through liquid-liquid phase separation (LLPS), resulting in the creation of condensates. From neurodegenerative disorders, cardiovascular diseases, aging, and metabolism to cancer, the influence of MLOs on human health and disease extends widely. This review discusses the underlying mechanisms of LLPS, the biophysical properties that drive MLO formation, and their implications for cellular function. We highlight recent advances in understanding how the physicochemical environment, molecular interactions, and post-translational modifications regulate LLPS and MLO dynamics. This review offers an overview of the discovery and current understanding of MLOs and biomolecular condensate in physiological conditions and diseases. This article aims to deliver the latest insights on MLOs and LLPS by analyzing current research, highlighting their critical role in cellular organization. The discussion also covers the role of membrane-associated condensates in cell signaling, including those involving T-cell receptors, stress granules linked to lysosomes, and biomolecular condensates within the Golgi apparatus. Additionally, the potential of targeting LLPS in clinical settings is explored, highlighting promising avenues for future research and therapeutic interventions.

Quantification of serum TDP-43 and neurofilament light chain in patients with amyotrophic lateral sclerosis stratified by UNC13A genotype

Amyotrophic Lateral Sclerosis (ALS) is a fatal neurodegenerative condition affecting upper and/or lower motor neurons and characterized neuropathologically by TDP-43 proteinopathy. Given its role in ALS pathobiology, it is currently under debate whether TDP-43 might represent a suitable ALS biomarker to be measured in patients' biofluids. The rs12608932 A > C single nucleotide polymorphism in the UNC13A gene is a risk factor for ALS and patients homozygous for the high-risk C allele display a higher burden of TDP-43 neuropathology than homozygotes for the low-risk A allele, although the association with TDP-43 levels in biofluids has never been evaluated. In this study, we measured serum levels of TDP-43 and neurofilament light chain (NFL) by Simoa technology in a cohort of 69 ALS patients stratified according to the UNC13A rs12608932 genotype compared to 43 neurologically healthy controls. By multiple linear regression analysis, serum TDP-43 was significantly elevated in ALS patients compared to controls, with UNC13A AA and AC, but not CC, ALS patients showing higher serum TDP-43 levels than controls. We also confirmed that serum NFL concentration was increased in ALS patients, without any correlation with the UNC13A genotype. Our results indicate that serum TDP-43 is higher in ALS patients compared to controls and that, in contrast to NFL, this increase is specifically associated with the UNC13A rs12608932 AA and AC genotypes, but not with the high-risk CC genotype. Studies in larger cohorts will be needed to confirm these findings and to elucidate the biological link between serum TDP-43 levels and UNC13A genotype.

Blood-Based Biomarkers in Frontotemporal Dementia: A Narrative Review

This narrative review explores the current landscape of blood biomarkers in Frontotemporal dementia (FTD). Neurofilament light chain (NfL) may be useful in the differentiation of behavioral variant FTD from primary psychiatric disorders (PPDs) or dementia with Lewy bodies (DLB). In prodromal FTD and presymptomatic mutation carriers (GRN, MAPT, C9orf72), elevated NfL may herald pheno-conversion to full-blown dementia. Baseline NfL correlates with steeper neuroanatomical changes and cognitive, behavioral and functional decline, making NfL promising in monitoring disease progression. Phosphorylated neurofilament heavy chain (pNfH) levels have a potential limited role in the demarcation of the conversion stage to full-blown FTD. Combined NfL and pNfH measurements may allow a wider stage stratification. Total tau levels lack applicability in the framework of FTD. p-tau, on the other hand, is of potential value in the discrimination of FTD from Alzheimer's dementia. Progranulin concentrations could serve the identification of GRN mutation carriers. Glial fibrillary acidic protein (GFAP) may assist in the differentiation of PPDs from behavioral variant FTD and the detection of GRN mutation carriers (additional research is warranted). Finally, TAR DNA-binding protein-43 (TDP-43) appears to be a promising diagnostic biomarker for FTD. Its potential in distinguishing TDP-43 pathology from other FTD-related pathologies requires further research.

Focused Ultrasound for Neurodegenerative Diseases

Neurodegenerative diseases are a leading cause of death and disability and pose a looming global public health crisis. Despite progress in understanding biological and molecular factors associated with these disorders and their progression, effective disease modifying treatments are presently limited. Focused ultrasound (FUS) is an emerging therapeutic strategy for Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. In these contexts, applications of FUS include neuroablation, neuromodulation, and/or blood-brain barrier opening with and without facilitated intracerebral drug delivery. Here, the authors review preclinical evidence and current and emerging applications of FUS for neurodegenerative diseases and summarize future directions in the field.

Detailed Analysis of the Palmomental Reflex and Its Clinical Significance

PURPOSE

This comprehensive review thoroughly explores the clinical significance of the palmomental reflex (PMR) in neurological disorders. PMR is a primitive reflex that, when reemerging in adults, indicates underlying neurological dysfunction.

METHOD

The article elaborates on the clinical assessment techniques, neurophysiological basis, and applications of PMR in various neurological disorders, including neurodegenerative diseases, cerebrovascular disorders, traumatic brain injury, and multiple sclerosis.

FINDING

By understanding the modulation and suppression mechanisms of PMR, valuable insights into the specific neurological impairments associated with these disorders can be gained.

CONCLUSION

The potential of PMR as a diagnostic marker, prognostic indicator, and treatment monitoring tool is increasingly evident.

Lysosome quality control in health and neurodegenerative diseases

Lysosomes are acidic organelles involved in crucial intracellular functions, including the degradation of organelles and protein, membrane repair, phagocytosis, endocytosis, and nutrient sensing. Given these key roles of lysosomes, maintaining their homeostasis is essential for cell viability. Thus, to preserve lysosome integrity and functionality, cells have developed a complex intracellular system, called lysosome quality control (LQC). Several stressors may affect the integrity of lysosomes, causing Lysosomal membrane permeabilization (LMP), in which membrane rupture results in the leakage of luminal hydrolase enzymes into the cytosol. After sensing the damage, LQC either activates lysosome repair, or induces the degradation of the ruptured lysosomes through autophagy. In addition, LQC stimulates the de novo biogenesis of functional lysosomes and lysosome exocytosis. Alterations in LQC give rise to deleterious consequences for cellular homeostasis. Specifically, the persistence of impaired lysosomes or the malfunctioning of lysosomal processes leads to cellular toxicity and death, thereby contributing to the pathogenesis of different disorders, including neurodegenerative diseases (NDs). Recently, several pieces of evidence have underlined the importance of the role of lysosomes in NDs. In this review, we describe the elements of the LQC system, how they cooperate to maintain lysosome homeostasis, and their implication in the pathogenesis of different NDs.

A scoping review of the unique landscape and challenges associated with dementia in the Western Pacific region

Dementia is a leading public health crisis that is projected to affect 152.8 million individuals by 2050, over half of whom will be living in the Western Pacific region. To determine the challenges and opportunities for capacity building in the region, this scoping review searched databases. Our findings reveal national and ethnoracial differences in the prevalence, literacy and genetic risk factors associated with dementia syndromes, underscoring the need to identify and mitigate relevant risk factors in this region. Importantly, ∼80% of research was derived from higher income countries, where the establishment of patient registries and biobanks reflect increased efforts and allocation of resources towards understanding the pathogenesis of dementia. We discuss the need for increased public awareness through culturally-relevant policies, the potential to support patients and caregivers through digital strategies and development of regional networks to mitigate the growing social impact and economic burden of dementia in this region.

Funding

FightMND Mid-Career Fellowship, NHMRC EL1 Fellowship, NHMRC Practitioner Fellowship (1156093), NHMRC Postgraduate scholarship (2022387).

Activation of the Keap1/Nrf2 pathway suppresses mitochondrial dysfunction, oxidative stress, and motor phenotypes in C9orf72 ALS/FTD models

Mitochondrial dysfunction is a common feature of C9orf72 amyotrophic lateral sclerosis/frontotemporal dementia (ALS/FTD); however, it remains unclear whether this is a cause or consequence of the pathogenic process. Analysing multiple aspects of mitochondrial biology across several Drosophila models of C9orf72-ALS/FTD, we found morphology, oxidative stress, and mitophagy are commonly affected, which correlated with progressive loss of locomotor performance. Notably, only genetic manipulations that reversed the oxidative stress levels were also able to rescue C9orf72 locomotor deficits, supporting a causative link between mitochondrial dysfunction, oxidative stress, and behavioural phenotypes. Targeting the key antioxidant Keap1/Nrf2 pathway, we found that genetic reduction of Keap1 or pharmacological inhibition by dimethyl fumarate significantly rescued the C9orf72-related oxidative stress and motor deficits. Finally, mitochondrial ROS levels were also elevated in C9orf72 patient-derived iNeurons and were effectively suppressed by dimethyl fumarate treatment. These results indicate that mitochondrial oxidative stress is an important mechanistic contributor to C9orf72 pathogenesis, affecting multiple aspects of mitochondrial function and turnover. Targeting the Keap1/Nrf2 signalling pathway to combat oxidative stress represents a therapeutic strategy for C9orf72-related ALS/FTD.

Directionality bias underpins divergent spatiotemporal progression of Alzheimer-related tauopathy in mouse models

Mounting evidence implicates trans-synaptic connectome-based spread as a shared mechanism behind different tauopathic conditions, yet also suggests there is divergent spatiotemporal progression between them. A potential parsimonious explanation for this apparent contradiction could be that different conditions incur differential rates and directional biases in tau transmission along fiber tracts. In this meta-analysis we closely examined this hypothesis and quantitatively tested it using spatiotemporal tau pathology patterns from 11 distinct models across 4 experimental studies. For this purpose, we extended a network-based spread model by incorporating net directionality along the connectome. Our data unambiguously supports the directional transmission hypothesis. First, retrograde bias is an unambiguously better predictor of tau progression than anterograde bias. Second, while spread exhibits retrograde character, our best-fitting biophysical models incorporate the mixed effects of both retrograde- and anterograde-directed spread, with notable tau-strain-specific differences. We also found a nontrivial association between directionality bias and tau strain aggressiveness, with more virulent strains exhibiting less retrograde character. Taken together, our study implicates directional transmission bias in tau transmission along fiber tracts as a general feature of tauopathy spread and a strong candidate explanation for the diversity of spatiotemporal tau progression between conditions. This simple and parsimonious mechanism may potentially fill a critical gap in our knowledge of the spatiotemporal ramification of divergent tauopathies.

Oculomotor atypicalities in motor neurone disease: a systematic review

Introduction

Cognitive dysfunction is commonplace in Motor Neurone Disease (MND). However, due to the prominent motor symptoms in MND, assessing patients' cognitive function through traditional cognitive assessments, which oftentimes require motoric responses, may become increasingly challenging as the disease progresses. Oculomotor pathways are apparently resistant to pathological degeneration in MND. As such, abnormalities in oculomotor functions, largely driven by cognitive processes such as saccades and smooth pursuit eye movement, may be reflective of frontotemporal cognitive deficits in MND. Thus, saccadic and smooth pursuit eye movements may prove to be ideal mechanistic markers of cognitive function in MND.

Methods

To ascertain the utility of saccadic and smooth pursuit eye movements as markers of cognitive function in MND, this review summarizes the literature concerning saccadic and smooth pursuit eye movement task performance in people with MND.

Results and discussion

Of the 22 studies identified, noticeable patterns suggest that people with MND can be differentiated from controls based on antisaccade and smooth pursuit task performance, and thus the antisaccade task and smooth pursuit task may be potential candidates for markers of cognition in MND. However, further studies which ascertain the concordance between eye tracking measures and traditional measures of cognition are required before this assumption is extrapolated, and clinical recommendations are made.

Systematic review registration

https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=376620, identifier CRD42023376620.

Comprehensive assessment of TDP-43 neuropathology data in the National Alzheimer's Coordinating Center database

TDP-43 proteinopathy is a salient neuropathologic feature in a subset of frontotemporal lobar degeneration (FTLD-TDP), in amyotrophic lateral sclerosis (ALS-TDP), and in limbic-predominant age-related TDP-43 encephalopathy neuropathologic change (LATE-NC), and is associated with hippocampal sclerosis of aging (HS-A). We examined TDP-43-related pathology data in the National Alzheimer's Coordinating Center (NACC) in two parts: (I) availability of assessments, and (II) associations with clinical diagnoses and other neuropathologies in those with all TDP-43 measures available. Part I: Of 4326 participants with neuropathology data collected using forms that included TDP-43 assessments, data availability was highest for HS-A (97%) and ALS (94%), followed by FTLD-TDP (83%). Regional TDP-43 pathologic assessment was available for 77% of participants, with hippocampus the most common region. Availability for the TDP-43-related measures increased over time, and was higher in centers with high proportions of participants with clinical FTLD. Part II: In 2142 participants with all TDP-43-related assessments available, 27% of participants had LATE-NC, whereas ALS-TDP or FTLD-TDP (ALS/FTLD-TDP) was present in 9% of participants, and 2% of participants had TDP-43 related to other pathologies ("Other TDP-43"). HS-A was present in 14% of participants, of whom 55% had LATE-NC, 20% ASL/FTLD-TDP, 3% Other TDP-43, and 23% no TDP-43. LATE-NC, ALS/FTLD-TDP, and Other TDP-43, were each associated with higher odds of dementia, HS-A, and hippocampal atrophy, compared to those without TDP-43 pathology. LATE-NC was associated with higher odds for Alzheimer's disease (AD) clinical diagnosis, AD neuropathologic change (ADNC), Lewy bodies, arteriolosclerosis, and cortical atrophy. ALS/FTLD-TDP was associated with higher odds of clinical diagnoses of primary progressive aphasia and behavioral-variant frontotemporal dementia, and cortical/frontotemporal lobar atrophy. When using NACC data for TDP-43-related analyses, researchers should carefully consider the incomplete availability of the different regional TDP-43 assessments, the high frequency of participants with ALS/FTLD-TDP, and the presence of other forms of TDP-43 pathology.

Pathology of neurodegenerative disease for the general neurologist

Neurodegeneration refers to progressive dysfunction or loss of selectively vulnerable neurones from brain and spinal cord regions. Despite important advances in fluid and imaging biomarkers, the definitive diagnosis of most neurodegenerative diseases still relies on neuropathological examination. Not only has careful clinicopathological correlation shaped current clinical diagnostic criteria and informed our understanding of the natural history of neurodegenerative diseases, but it has also identified conditions with important public health implications, including variant Creutzfeldt-Jakob disease, iatrogenic amyloid-β and chronic traumatic encephalopathy. Neuropathological examination may also point to previously unsuspected genetic diagnoses with potential implications for living relatives. Moreover, detailed neuropathological assessment is crucial for research studies that rely on curated postmortem tissue to investigate the molecular mechanisms responsible for neurodegeneration and for biomarker discovery and validation. This review aims to elucidate the hallmark pathological features of neurodegenerative diseases commonly seen in general neurology clinics, such as Alzheimer's disease and Parkinson's disease; rare but well-known diseases, including progressive supranuclear palsy, corticobasal degeneration and multiple system atrophy and more recently described entities such as chronic traumatic encephalopathy and age-related tau astrogliopathy.

Amyotrophic lateral sclerosis; clinical features, differential diagnosis and pathology

Amyotrophic lateral sclerosis (ALS) is a late-onset syndrome characterized by the progressive degeneration of both upper motor neurons (UMN) and lower motor neurons (LMN). ALS forms a clinical continuum with frontotemporal dementia (FTD), in which there are progressive language deficits or behavioral changes. The genetics and pathology underlying both ALS and FTD overlap as well, with cytoplasmatic misvocalization of TDP-43 as the hallmark. ALS is diagnosed by exclusion. Over the years several diagnostic criteria have been proposed, which in essence all require a history of slowly progressive motor symptoms, with UMN and LMN signs on neurological examination, clear spread of symptoms through the body, the exclusion of other disorder that cause similar symptoms and an EMG that it is compatible with LMN loss. ALS is heterogeneous disorder that may present in multitude ways, which makes the diagnosis challenging. Therefore, a systematic approach in the diagnostic process is required in line with the most common presentations. Subsequently, assessing whether there are cognitive and/or behavioral changes within the spectrum of FTD and lastly determining the cause is genetic. This chapter, an outline on how to navigate this 3 step process.

Targeting 14-3-3θ-mediated TDP-43 pathology in amyotrophic lateral sclerosis and frontotemporal dementia mice

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are characterized by cytoplasmic deposition of the nuclear TAR-binding protein 43 (TDP-43). Although cytoplasmic re-localization of TDP-43 is a key event in the pathogenesis of ALS/FTD, the underlying mechanisms remain unknown. Here, we identified a non-canonical interaction between 14-3-3θ and TDP-43, which regulates nuclear-cytoplasmic shuttling. Neuronal 14-3-3θ levels were increased in sporadic ALS and FTD with TDP-43 pathology. Pathogenic TDP-43 showed increased interaction with 14-3-3θ, resulting in cytoplasmic accumulation, insolubility, phosphorylation, and fragmentation of TDP-43, resembling pathological changes in disease. Harnessing this increased affinity of 14-3-3θ for pathogenic TDP-43, we devised a gene therapy vector targeting TDP-43 pathology, which mitigated functional deficits and neurodegeneration in different ALS/FTD mouse models expressing mutant or non-mutant TDP-43, including when already symptomatic at the time of treatment. Our study identified 14-3-3θ as a mediator of cytoplasmic TDP-43 localization with implications for ALS/FTD pathogenesis and therapy.

Current perspectives on neuromodulation in ALS patients: A systematic review and meta-analysis

Amyotrophic Lateral Sclerosis (ALS) is a progressive neurodegenerative disease that affects motor neurons, resulting in muscle weakness, paralysis, and eventually patient mortality. In recent years, neuromodulation techniques have emerged as promising potential therapeutic approaches to slow disease progression and improve the quality of life of ALS patients. A systematic review was conducted until August 8, 2023, to evaluate the neuromodulation methods used and their potential in the treatment of ALS. The search strategy was applied in the Cochrane Central database, incorporating results from other databases such as PubMed, Embase, CTgov, CINAHL, and ICTRP. Following the exclusion of papers that did not fulfil the inclusion criteria, a total of 2090 records were found, leaving a total of 10 studies. R software was used to conduct meta-analyses based on the effect sizes between the experimental and control groups. This revealed differences in muscle stretch measures with manual muscle testing (p = 0.012) and resting motor threshold (p = 0.0457), but not with voluntary isometric contraction (p = 0.1883). The functionality of ALS was also different (p = 0.007), but not the quality of life. Although intracortical facilitation was not seen in motor cortex 1 (M1) (p = 0.1338), short-interval intracortical inhibition of M1 was significant (p = 0.0001). BDNF showed no differences that were statistically significant (p = 0.2297). Neuromodulation-based treatments are proposed as a promising therapeutic approach for ALS that can produce effects on muscle function, spasticity, and intracortical connections through electrical, magnetic, and photonic stimulation. Photobiomodulation stands out as an innovative approach that uses specific wavelengths to influence mitochondria, with the aim of improving mitochondrial function and reducing excitotoxicity. The lack of reliable placebo controls and the variation in stimulation frequency are some of the drawbacks of neuromodulation.

Familial motor neuron disease: co-occurrence of PLS and ALS (-FTD)

OBJECTIVE

To report the frequency and characteristics of patients diagnosed with primary lateral sclerosis (PLS) with a positive family history for motor neuron diseases (MND) in the Netherlands and to compare our findings to the literature.

METHODS

Patients were identified through our ongoing, prospective population-based study on MND in The Netherlands, which also includes a standardized collection of patient characteristics, genetic testing, and family history. Only patients meeting the latest consensus criteria for definite PLS were included. The family history was considered positive for MND if any family members had been diagnosed with PLS, amyotrophic lateral sclerosis (ALS)(-FTD), or progressive muscular atrophy (PMA). Additionally, the literature was reviewed on PLS cases in which MND co-occurred within the same family.

RESULTS

We identified 392 definite PLS cases, resulting in 9 families with a PLS patient and a positive family history for MND (2.3%). In only one of these pedigrees, a pathogenic variant (C9orf72 repeat expansion) was found. Our literature review revealed 23 families with a co-occurrence of PLS and MND, with 12 of them having a potentially pathogenic genetic variant.

CONCLUSIONS

The consistent observation of PLS patients with a positive family history for MND, evident in both our study and the literature, implies the presence of shared underlying genetic factors between PLS and ALS. However, these factors are yet to be elucidated.

Diagnostic utility of transcranial magnetic stimulation for neurodegenerative disease: a critical review

Neurodegenerative diseases pose significant challenges due to their impact on brain structure, function, and cognition. As life expectancy rises, the prevalence of these disorders is rapidly increasing, resulting in substantial personal, familial, and societal burdens. Efforts have been made to optimize the diagnostic and therapeutic processes, primarily focusing on clinical, cognitive, and imaging characterization. However, the emergence of non-invasive brain stimulation techniques, specifically transcranial magnetic stimulation (TMS), offers unique functional insights and diagnostic potential. TMS allows direct evaluation of brain function, providing valuable information inaccessible through other methods. This review aims to summarize the current and potential diagnostic utility of TMS in investigating neurodegenerative diseases, highlighting its relevance to the field of cognitive neuroscience. The findings presented herein contribute to the growing body of research focused on improving our understanding and management of these debilitating conditions, particularly in regions with limited resources and a pressing need for innovative approaches.

History of ALS and the competing theories on pathogenesis: IFCN handbook chapter

Amyotrophic lateral sclerosis (ALS) is a rapidly progressive neurodegenerative disorder of the human motor system, first described in the 19th Century. The etiology of ALS appears to be multifactorial, with a complex interaction of genetic, epigenetic, and environmental factors underlying the onset of disease. Importantly, there are no known naturally occurring animal models, and transgenic mouse models fail to faithfully reproduce ALS as it manifests in patients. Debate as to the site of onset of ALS remain, with three competing theories proposed, including (i) the dying-forward hypothesis, whereby motor neuron degeneration is mediated by hyperexcitable corticomotoneurons via an anterograde transsynaptic excitotoxic mechanism, (ii) dying-back hypothesis, proposing the ALS begins in the peripheral nervous system with a toxic factor(s) retrogradely transported into the central nervous system and mediating upper motor neuron dysfunction, and (iii) independent hypothesis, suggesting that upper and lower motor neuron degenerated independently. Transcranial magnetic stimulation studies, along with pathological and genetic findings have supported the dying forward hypothesis theory, although the science is yet to be settled. The review provides a historical overview of ALS, discusses phenotypes and likely pathogenic mechanisms.

Non-motor symptoms in motor neuron disease: prevalence, assessment and impact

People with motor neuron disease often experience non-motor symptoms that may occur secondary to, or distinct from, motor degeneration and that may significantly reduce quality of life, despite being under-recognized and evaluated in clinical practice. Non-motor symptoms explored in this population-based study include pain, fatigue, gastrointestinal issues, poor sleep, low mood, anxiety, problematic saliva, apathy, emotional lability, cognitive complaints and sexual dysfunction. People registered on the Clinical Audit Research and Evaluation of motor neuron disease platform, the Scottish Motor Neuron Disease Register, were invited to complete a questionnaire on non-motor symptoms and a self-reported Amyotrophic Lateral Sclerosis Functional Rating Scale. The questionnaire comprised a pre-defined list of 11 potential non-motor symptoms, with the opportunity to list additional symptoms. A total of 120 individuals participated in this cross-sectional study, a 39% response rate of those sent questionnaires (n = 311); 99% of participants recruited (n = 120) experienced at least one non-motor symptom, with 72% (n = 120) reporting five or more. The symptoms most often reported were pain and fatigue (reported by 76% of participants, respectively). The symptoms reported to be most impactful were gastrointestinal issues (reported as 'severe' by 54% of participants who experienced them), followed by pain and problematic saliva (51%, respectively). Lower Amyotrophic Lateral Sclerosis Functional Rating Scale scores, indicating more advanced disease and being a long survivor [diagnosed over 8 years ago; Black et al. (Genetic epidemiology of motor neuron disease-associated variants in the Scottish population. Neurobiol Aging. 2017;51:178.e11-178.e20.)], were significantly associated with reporting more symptoms; 73% of respondents were satisfied with the frequency that non-motor symptoms were discussed in clinical care; 80% of participants indicated they believe evaluation of non-motor symptom is important to include as outcomes in trials, independent of their personal experience of these symptoms. The preferred method of assessment was completing questionnaires, at home. The overwhelming majority of people with motor neuron disease report non-motor symptoms and these frequently co-occur. Pain, fatigue, gastrointestinal issues, sleep, mood, anxiety, problematic saliva, apathy, emotional lability, cognitive complaints and sexual dysfunction are prevalent. People with motor neuron disease who had worse physical function and those who were long survivors were more likely to report more symptoms. Where reported, these symptoms are frequent, impactful and a priority for people with motor neuron disease in clinical care and trial design.

Evaluation of an educational conference for persons affected by hereditary frontotemporal degeneration and amyotrophic lateral sclerosis

Objective

There are limited studies exploring the support and education needs of individuals at-risk for or diagnosed with hereditary frontotemporal degeneration (FTD) and/or amyotrophic lateral sclerosis (ALS). This study evaluated a novel conference for this population to assess conference efficacy, probe how participants assessed relevant resources, and identify outstanding needs of persons at-risk/diagnosed.

Methods

We implemented a post-conference electronic survey that probed participants' satisfaction, prior experience with resources, and unmet needs. Along with multiple-choice, free-text items were included to gather qualitative context.

Results

Survey completion rate was 31% (115/376 attendees who were emailed the survey). There was positive interest in pursuing genetic counseling among eligible responders: 61% indicated they planned to seek genetic counseling because of the conference, which was significantly more than those who were undecided (21%) or did not plan to seek genetic counseling (18%). Qualitative data demonstrated need for additional education, support, and research opportunities.

Conclusion

Conference reactions indicate this is a valued resource. Results indicated the importance of raising awareness about existing resources, and the need for further resource development, especially for at-risk communities.

Innovation

While most resources are developed for caregivers' needs, this unique program targets at-risk individuals and unites ALS and FTD communities.

Repeated mild traumatic brain injury triggers pathology in asymptomatic C9ORF72 transgenic mice

Frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) are fatal neurodegenerative diseases that represent ends of the spectrum of a single disease. The most common genetic cause of FTD and ALS is a hexanucleotide repeat expansion in the C9orf72 gene. Although epidemiological data suggest that traumatic brain injury (TBI) represents a risk factor for FTD and ALS, its role in exacerbating disease onset and course remains unclear. To explore the interplay between traumatic brain injury and genetic risk in the induction of FTD/ALS pathology we combined a mild repetitive traumatic brain injury paradigm with an established bacterial artificial chromosome transgenic C9orf72 (C9BAC) mouse model without an overt motor phenotype or neurodegeneration. We assessed 8-10 week-old littermate C9BACtg/tg (n = 21), C9BACtg/- (n = 20) and non-transgenic (n = 21) mice of both sexes for the presence of behavioural deficits and cerebral histopathology at 12 months after repetitive TBI. Repetitive TBI did not affect body weight gain, general neurological deficit severity, nor survival over the 12-month observation period and there was no difference in rotarod performance, object recognition, social interaction and acoustic characteristics of ultrasonic vocalizations of C9BAC mice subjected to repetitive TBI versus sham injury. However, we found that repetitive TBI increased the time to the return of the righting reflex, reduced grip force, altered sociability behaviours and attenuated ultrasonic call emissions during social interactions in C9BAC mice. Strikingly, we found that repetitive TBI caused widespread microglial activation and reduced neuronal density that was associated with loss of histological markers of axonal and synaptic integrity as well as profound neuronal transactive response DNA binding protein 43 kDa mislocalization in the cerebral cortex of C9BAC mice at 12 months; this was not observed in non-transgenic repetitive TBI and C9BAC sham mice. Our data indicate that repetitive TBI can be an environmental risk factor that is sufficient to trigger FTD/ALS-associated neuropathology and behavioural deficits, but not paralysis, in mice carrying a C9orf72 hexanucleotide repeat expansion.

Artificial intelligence for dementia drug discovery and trials optimization

Drug discovery and clinical trial design for dementia have historically been challenging. In part these challenges have arisen from patient heterogeneity, length of disease course, and the tractability of a target for the brain. Applying big data analytics and machine learning tools for drug discovery and utilizing them to inform successful clinical trial design has the potential to accelerate progress. Opportunities arise at multiple stages in the therapy pipeline and the growing availability of large medical data sets opens possibilities for big data analyses to answer key questions in clinical and therapeutic challenges. However, before this goal is reached, several challenges need to be overcome and only a multi-disciplinary approach can promote data-driven decision-making to its full potential. Herein we review the current state of machine learning applications to clinical trial design and drug discovery, while presenting opportunities and recommendations that can break down the barriers to implementation.

Advances in molecular pathology, diagnosis, and treatment of amyotrophic lateral sclerosis

Although the past two decades have produced exciting discoveries in the genetics and pathology of amyotrophic lateral sclerosis (ALS), progress in developing an effective therapy remains slow. This review summarizes the critical discoveries and outlines the advances in disease characterization, diagnosis, imaging, and biomarkers, along with the current status of approaches to ALS care and treatment. Additional knowledge of the factors driving disease progression and heterogeneity will hopefully soon transform the care for patients with ALS into an individualized, multi-prong approach able to prevent disease progression sufficiently to allow for a dignified life with limited disability.

RNA-binding deficient TDP-43 drives cognitive decline in a mouse model of TDP-43 proteinopathy

TDP-43 proteinopathies including frontotemporal lobar degeneration (FTLD) and amyotrophic lateral sclerosis (ALS) are neurodegenerative disorders characterized by aggregation and mislocalization of the nucleic acid-binding protein TDP-43 and subsequent neuronal dysfunction. Here, we developed endogenous models of sporadic TDP-43 proteinopathy based on the principle that disease-associated TDP-43 acetylation at lysine 145 (K145) alters TDP-43 conformation, impairs RNA-binding capacity, and induces downstream mis-regulation of target genes. Expression of acetylation-mimic TDP-43K145Q resulted in stress-induced nuclear TDP-43 foci and loss of TDP-43 function in primary mouse and human-induced pluripotent stem cell (hiPSC)-derived cortical neurons. Mice harboring the TDP-43K145Q mutation recapitulated key hallmarks of FTLD, including progressive TDP-43 phosphorylation and insolubility, TDP-43 mis-localization, transcriptomic and splicing alterations, and cognitive dysfunction. Our study supports a model in which TDP-43 acetylation drives neuronal dysfunction and cognitive decline through aberrant splicing and transcription of critical genes that regulate synaptic plasticity and stress response signaling. The neurodegenerative cascade initiated by TDP-43 acetylation recapitulates many aspects of human FTLD and provides a new paradigm to further interrogate TDP-43 proteinopathies.

The association between lifelong personality and clinical phenotype in the FTD-ALS spectrum

Introduction

Frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) are two phenotypes of the same neurodegenerative disease, the FTD-ALS spectrum. What determines the development of one rather than the other phenotype is still unknown. Based on the clinical observation that patients' personality seems to differ between the two phenotypes, i.e., ALS patients tend to display kind, prosocial behaviors whereas FTD patients tend to present anti-social behaviors, and that these traits are often reported as pre-existing the disease onset by caregivers, we set up to study experimentally patients' personality in their premorbid life.

Methods

We first tested for differences between groups, then tested the association between premorbid personality and current functional organization of the brain. Premorbid personality of a cohort of forty patients, 27 FTD and 13 ALS, was explored through the NEO Personality Inventory 3 (NEO-PI-3), which analyses the five main personality factors, completed by the caregiver with reference to patient's personality 20 years before symptoms onset (premorbid). A subgroup of patients underwent a brain MRI including structural and resting-state functional MRI (rsfMRI).

Results

A significant difference between FTD and ALS in premorbid personality emerged in the Openness (133.92 FTD vs. 149.84 ALS, p = 0.01) and Extraversion (136.55 FTD vs. 150.53 ALS, p = 0.04) factors. This suggests that ALS patients had been, in their premorbid life, more open to new experiences, more sociable and optimistic than FTD patients. They also showed greater functional connectivity than both FTD and a control group in the Salience resting state network, over and above differences in gray matter atrophy. Finally, there was a positive correlation between premorbid Openness and functional connectivity in the Salience network across all patients, suggesting a possible association between premorbid personality and current functional organization of the brain, irrespective of the degree of atrophy.

Discussion

Our proof-of-concept results suggest that premorbid personality may eventually predispose to the development of one, rather than the other, phenotype in the FTD-ALS spectrum.

Regional spreading pattern is associated with clinical phenotype in amyotrophic lateral sclerosis

Increasing evidence shows that disease spreading in amyotrophic lateral sclerosis (ALS) follows a preferential pattern with more frequent involvement of contiguous regions from the site of symptom onset. The aim of our study was to assess if: (i) the burden of upper (UMN) and lower motor neuron (LMN) involvement influences directionality of disease spreading; (ii) specific patterns of disease progression are associated with motor and neuropsychological features of different ALS subtypes (classic, bulbar, primary lateral sclerosis, UMN-predominant, progressive muscular atrophy, flail arm, flail leg); and (iii) specific clinical features may help identify ALS subtypes, which remain localized to the site of onset for a prolonged time (regionally entrenching ALS). A single-centre, retrospective cohort of 913 Italian ALS patients was evaluated to assess correlations between directionality of the disease process after symptom onset and motor/neuropsychological phenotype. All patients underwent an extensive evaluation including the following clinical scales: Penn Upper Motor Neuron Score (PUMNS), MRC Scale for Muscle Strength and the Edinburgh Cognitive and Behavioural ALS Screen (ECAS). The most frequent initial spreading pattern was that towards adjacent horizontal regions (77.3%), which occurred preferentially in patients with lower MRC scores (P = 0.038), while vertical diffusion (21.1%) was associated with higher PUMNS (P < 0.001) and with reduced survival (P < 0.001). Non-contiguous disease spreading was associated with more severe UMN impairment (P = 0.003), while contiguous disease pattern with lower MRC scores. Furthermore, non-contiguous disease spreading was associated with more severe cognitive impairment in both executive and visuospatial ECAS domains. Individuals with regionally entrenching ALS were more frequently female (45.6% versus 36.9%; P = 0.028) and had higher frequencies of symmetric disease onset (40.3% versus 19.7%; P < 0.001) and bulbar phenotype (38.5% versus 16.4%; P < 0.001). Our study suggests that motor phenotypes characterized by a predominant UMN involvement are associated with a vertical pattern of disease progression reflecting ipsilateral spreading within the motor cortex, while those with predominant LMN involvement display more frequently a horizontal spreading from one side of the spinal cord to the other. These observations raise the hypothesis that one of the mechanisms underlying disease spreading in ALS pathology is represented by diffusion of toxic factors in the neuron microenvironment. Finally, it is possible that in our cohort, regionally entrenching ALS forms are mainly observed in patients with atypical bulbar phenotypes, characterized by a slowly progressive course and relatively benign prognosis.

C9ORF72 Gene GGGGCC Hexanucleotide Expansion: A High Clinical Variability from Amyotrophic Lateral Sclerosis to Frontotemporal Dementia

The expanded GGGGCC hexanucleotide repeat (HRE) in the non-coding region of the C9ORF72 gene (C9ORF72-HRE) is the most common genetic cause of familial forms of amyotrophic lateral sclerosis (ALS), FTD, and concurrent ALS and FTD (ALS-FTD), in addition to contributing to the sporadic forms of these diseases. Both syndromes overlap not only genetically, but also sharing similar clinical and neuropathological findings, being considered as a spectrum. In this paper we describe the clinical-genetic findings in a Basque family with different manifestations within the spectrum, our difficulties in reaching the diagnosis, and a narrative review, carried out as a consequence, of the main features associated with C9ORF72-HRE. Family members underwent a detailed clinical assessment, neurological examination, and genetic analysis by repeat-primed PCR. We studied 10 relatives of a symptomatic carrier of the C9ORF72-HRE expansion. Two of them presented the expansion in the pathological range, one of them was symptomatic whereas the other one remained asymptomatic at 72 years. Given the great intrafamilial clinical variability of C9ORF72-HRE, the characterization of patients and family members with particular clinical and genetic subgroups within ALS and FTD becomes a bottleneck for medication development, in particular for genetically focused medicines for ALS and FTD.

A toxic gain-of-function mechanism in C9orf72 ALS impairs the autophagy-lysosome pathway in neurons

BACKGROUND

Motor neurons (MNs), which are primarily affected in amyotrophic lateral sclerosis (ALS), are a specialized type of neurons that are long and non-dividing. Given their unique structure, these cells heavily rely on transport of organelles along their axons and the process of autophagy to maintain their cellular homeostasis. It has been shown that disruption of the autophagy pathway is sufficient to cause progressive neurodegeneration and defects in autophagy have been associated with various subtypes of ALS, including those caused by hexanucleotide repeat expansions in the C9orf72 gene. A more comprehensive understanding of the dysfunctional cellular mechanisms will help rationalize the design of potent and selective therapies for C9orf72-ALS.

METHODS

In this study, we used induced pluripotent stem cell (iPSC)-derived MNs from C9orf72-ALS patients and isogenic control lines to identify the underlying mechanisms causing dysregulations of the autophagy-lysosome pathway. Additionally, to ascertain the potential impact of C9orf72 loss-of-function on autophagic defects, we characterized the observed phenotypes in a C9orf72 knockout iPSC line (C9-KO).

RESULTS

Despite the evident presence of dysfunctions in several aspects of the autophagy-lysosome pathway, such as disrupted lysosomal homeostasis, abnormal lysosome morphology, inhibition of autophagic flux, and accumulation of p62 in C9orf72-ALS MNs, we were surprised to find that C9orf72 loss-of-function had minimal influence on these phenotypes. Instead, we primarily observed impairment in endosome maturation as a result of C9orf72 loss-of-function. Additionally, our study shed light on the pathological mechanisms underlying C9orf72-ALS, as we detected an increased TBK1 phosphorylation at S172 in MNs derived from C9orf72 ALS patients.

CONCLUSIONS

Our data provides further insight into the involvement of defects in the autophagy-lysosome pathway in C9orf72-ALS and strongly indicate that those defects are mainly due to the toxic gain-of-function mechanisms underlying C9orf72-ALS.

DHX9/DNA-tandem repeat-dependent downregulation of ciRNA-Fmn1 in the dorsal horn is required for neuropathic pain

Circular RNAs (ciRNAs) are emerging as new players in the regulation of gene expression. However, how ciRNAs are involved in neuropathic pain is poorly understood. Here, we identify the nervous-tissue-specific ciRNA-Fmn1 and report that changes in ciRNA-Fmn1 expression in spinal cord dorsal horn neurons play a key role in neuropathic pain after nerve injury. ciRNA-Fmn1 was significantly downregulated in ipsilateral dorsal horn neurons after peripheral nerve injury, at least in part because of a decrease in DNA helicase 9 (DHX9), which regulates production of ciRNA-Fmn1 by binding to DNA-tandem repeats. Blocking ciRNA-Fmn1 downregulation reversed nerve-injury-induced reductions in both the binding of ciRNA-Fmn1 to the ubiquitin ligase UBR5 and the level of ubiquitination of albumin (ALB), thereby abrogating the nerve-injury-induced increase of ALB expression in the dorsal horn and attenuating the associated pain hypersensitivities. Conversely, mimicking downregulation of ciRNA-Fmn1 in naïve mice reduced the UBR5-controlled ubiquitination of ALB, leading to increased expression of ALB in the dorsal horn and induction of neuropathic-pain-like behaviors in naïve mice. Thus, ciRNA-Fmn1 downregulation caused by changes in binding of DHX9 to DNA-tandem repeats contributes to the genesis of neuropathic pain by negatively modulating UBR5-controlled ALB expression in the dorsal horn.

Limbic-predominant age-related TDP43 encephalopathy (LATE) neuropathological change in neurodegenerative diseases

TAR DNA-binding protein 43 (TDP43) is a focus of research in late-onset dementias. TDP43 pathology in the brain was initially identified in amyotrophic lateral sclerosis and frontotemporal lobar degeneration, and later in Alzheimer disease (AD), other neurodegenerative diseases and ageing. Limbic-predominant age-related TDP43 encephalopathy (LATE), recognized as a clinical entity in 2019, is characterized by amnestic dementia resembling AD dementia and occurring most commonly in adults over 80 years of age. Neuropathological findings in LATE, referred to as LATE neuropathological change (LATE-NC), consist of neuronal and glial cytoplasmic TDP43 localized predominantly in limbic areas with or without coexisting hippocampal sclerosis and/or AD neuropathological change and without frontotemporal lobar degeneration or amyotrophic lateral sclerosis pathology. LATE-NC is frequently associated with one or more coexisting pathologies, mainly AD neuropathological change. The focus of this Review is the pathology, genetic risk factors and nature of the cognitive impairments and dementia in pure LATE-NC and in LATE-NC associated with coexisting pathologies. As the clinical and cognitive profile of LATE is currently not easily distinguishable from AD dementia, it is important to develop biomarkers to aid in the diagnosis of this condition in the clinic. The pathogenesis of LATE-NC should be a focus of future research to form the basis for the development of preventive and therapeutic strategies.

Survival in sporadic ALS is associated with lower p62 burden in the spinal cord

The autophagy marker p62 appears as a consistent component of pathological aggregates in amyotrophic lateral sclerosis (ALS) and its modulation to facilitate protein degradation has been proposed as a potential therapeutic target. Importantly, recent studies have implicated diffuse phosphorylated TDP-43 inclusions that are immuno-negative for p62 in more rapid disease, highlighting the need for better understanding of p62 involvement in ALS pathogenesis. The present study set out to assess p62 pathology in the motor neurons of 31 patients with sporadic ALS that had either a short (<2 years) or longer (4-7 years) disease duration to determine its association with pTDP-43 pathology, motor neuron loss, and survival in sporadic disease. Our results identified significantly more cytoplasmic p62 aggregates in the spinal cord of patients with a shorter survival. Disease duration demonstrated a negative association with p62 burden and density of remaining motor neurons in the spinal cord, suggesting that survival in sporadic ALS is associated with the successful clearance of lower motor neurons with p62 aggregates. These findings implicate the autophagy pathway in ALS survival and provide support for further study of p62 as a potential prognostic biomarker in ALS.

Neuroinflammatory Pathways in the ALS-FTD Continuum: A Focus on Genetic Variants

Amyotrophic Lateral Sclerosis (ALS) and Frontotemporal dementia (FDT) are progressive neurodegenerative disorders that, in several cases, overlap in clinical presentation, and genetic and pathological disease mechanisms. About 10-15% of ALS cases and up to 40% of FTD are familial, usually with dominant traits. ALS and FTD, in several cases, share common gene mutations, such as in C9ORF72, TARDBP, SQSTM-1, FUS, VCP, CHCHD10, and TBK-1. Also, several mechanisms are involved in ALS and FTD pathogenesis, such as protein misfolding, oxidative stress, and impaired axonal transport. In addition, neuroinflammation and neuroinflammatory cells, such as astrocytes, oligodendrocytes, microglia, and lymphocytes and, overall, the cellular microenvironment, have been proposed as pivotal players in the pathogenesis the ALS-FTD spectrum disorders. This review overviews the current evidence regarding neuroinflammatory markers in the ALS/FTD continuum, focusing on the neuroinflammatory pathways involved in the genetic cases, moving from post-mortem reports to in vivo biofluid and neuroimaging data. We further discuss the potential link between genetic and autoimmune disorders and potential therapeutic implications.

UNC13A in amyotrophic lateral sclerosis: from genetic association to therapeutic target

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease with limited treatment options and an incompletely understood pathophysiology. Although genomewide association studies (GWAS) have advanced our understanding of the disease, the precise manner in which risk polymorphisms contribute to disease pathogenesis remains unclear. Of relevance, GWAS have shown that a polymorphism (rs12608932) in the UNC13A gene is associated with risk for both ALS and frontotemporal dementia (FTD). Homozygosity for the C-allele at rs12608932 modifies the ALS phenotype, as these patients are more likely to have bulbar-onset disease, cognitive impairment and FTD at baseline as well as shorter survival. UNC13A is expressed in neuronal tissue and is involved in maintaining synaptic active zones, by enabling the priming and docking of synaptic vesicles. In the absence of functional TDP-43, risk variants in UNC13A lead to the inclusion of a cryptic exon in UNC13A messenger RNA, subsequently leading to nonsense mediated decay, with loss of functional protein. Depletion of UNC13A leads to impaired neurotransmission. Recent discoveries have identified UNC13A as a potential target for therapy development in ALS, with a confirmatory trial with lithium carbonate in UNC13A cases now underway and future approaches with antisense oligonucleotides currently under consideration. Considering UNC13A is a potent phenotypic modifier, it may also impact clinical trial outcomes. This present review describes the path from the initial discovery of UNC13A as a risk gene in ALS to the current therapeutic options being explored and how knowledge of its distinct phenotype needs to be taken into account in future trials.

Propranolol reduces the accumulation of cytotoxic aggregates in C9orf72-ALS/FTD in vitro models

Mutations in the C9orf72 gene are the most common cause of familial amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). The pathogenetic mechanisms linked to this gene are a direct consequence of an aberrant intronic expansion of a GGGGCC hexanucleotide located between the 1a and 1b non-coding exons, which can be transcribed to form cytotoxic RNA foci or even translated into aggregation-prone dipeptide repeat proteins. Importantly, the abnormal length of these repeats affects also the expression levels of C9orf72 itself, which suggests haploinsufficiency as additional pathomechanism. Thus, it appears that both toxic gain of function and loss of function are distinct but still coexistent features contributing to the insurgence of the disease in case of C9orf72 mutations. In this study, we aimed at identifying a strategy to address both aspects of the C9orf72-related pathobiochemistry and provide proof-of-principle information for a better understanding of the mechanisms leading to neuronal loss. By using primary neurons overexpressing toxic poly(GA), the most abundant protein product of the GGGGCC repeats, we found that the antiarrhythmic drug propranolol could efficiently reduce the accumulation of aberrant aggregates and increase the survival of C9orf72-related cultures. Interestingly, the improved catabolism appeared to not depend on major degradative pathways such as autophagy and the proteasome. By analyzing the proteome of poly(GA)-expressing neurons after exposure to propranolol, we found that the drug increased lysosomal degradation through a mechanism directly involving C9orf72 protein, whose levels were increased after treatment. Further confirmation of the beneficial effect of the beta blocker on aggregates' accumulation and survival of hiPSC-derived C9orf72-mutant motoneurons strengthened the finding that addressing both facets of C9orf72 pathology might represent a valid strategy for the treatment of these ALS/FTD cases.

Loss of PML nuclear bodies in familial amyotrophic lateral sclerosis-frontotemporal dementia

Amyotrophic Lateral Sclerosis (ALS) and Frontotemporal Dementia (FTD) are two neurodegenerative disorders that share genetic causes and pathogenic mechanisms. The critical genetic players of ALS and FTD are the TARDBP, FUS and C9orf72 genes, whose protein products, TDP-43, FUS and the C9orf72-dipeptide repeat proteins, accumulate in form of cytoplasmic inclusions. The majority of the studies focus on the understanding of how cells control TDP-43 and FUS aggregation in the cytoplasm, overlooking how dysfunctions occurring at the nuclear level may influence the maintenance of protein solubility outside of the nucleus. However, protein quality control (PQC) systems that maintain protein homeostasis comprise a cytoplasmic and a nuclear arm that are interconnected and share key players. It is thus conceivable that impairment of the nuclear arm of the PQC may have a negative impact on the cytoplasmic arm of the PQC, contributing to the formation of the cytoplasmic pathological inclusions. Here we focused on two stress-inducible condensates that act as transient deposition sites for misfolding-prone proteins: Promyelocytic leukemia protein (PML) nuclear bodies (PML-NBs) and cytoplasmic stress granules (SGs). Upon stress, PML-NBs compartmentalize misfolded proteins, including defective ribosomal products (DRiPs), and recruit chaperones and proteasomes to promote their nuclear clearance. SGs transiently sequester aggregation-prone RNA-binding proteins linked to ALS-FTD and mRNAs to attenuate their translation. We report that PML assembly is impaired in the human brain and spinal cord of familial C9orf72 and FUS ALS-FTD cases. We also show that defective PML-NB assembly impairs the compartmentalization of DRiPs in the nucleus, leading to their accumulation inside cytoplasmic SGs, negatively influencing SG dynamics. Although it is currently unclear what causes the decrease of PML-NBs in ALS-FTD, our data highlight the existence of a cross-talk between the cytoplasmic and nuclear PQC systems, whose alteration can contribute to SG accumulation and cytoplasmic protein aggregation in ALS-FTD.

Memory-guided navigation in amyotrophic lateral sclerosis

BACKGROUND

Previous studies have yielded inconsistent results about hippocampal involvement in non-demented patients with amyotrophic lateral sclerosis (ALS). We hypothesized that testing of memory-guided spatial navigation i.e., a highly hippocampus-dependent behaviour, might reveal behavioural correlates of hippocampal dysfunction in non-demented ALS patients.

METHODS

We conducted a prospective study of spatial cognition in 43 non-demented ALS outpatients (11f, 32 m, mean age 60.0 years, mean disease duration 27.0 months, mean ALSFRS-R score 40.0) and 43 healthy controls (14f, 29 m, mean age 57.0 years). Participants were tested with a virtual memory-guided navigation task derived from animal research ("starmaze") that has previously been used in studies of hippocampal function. Participants were further tested with neuropsychological tests of visuospatial memory (SPART, 10/36 Spatial Recall Test), fluency (5PT, five-point test) and orientation (PTSOT, Perspective Taking/Spatial Orientation Test).

RESULTS

Patients successfully learned and navigated the starmaze from memory, both in conditions that forced memory of landmarks (success: patients 50.7%, controls 47.7%, p = 0.786) and memory of path sequences (success: patients 96.5%, controls 94.0%, p = 0.937). Measures of navigational efficacy (latency, path error and navigational uncertainty) did not differ between groups (p ≥ 0.546). Likewise, SPART, 5PT and PTSOT scores did not differ between groups (p ≥ 0.238).

CONCLUSIONS

This study found no behavioural correlate for hippocampal dysfunction in non-demented ALS patients. These findings support the view that the individual cognitive phenotype of ALS may relate to distinct disease subtypes rather than being a variable expression of the same underlying condition.