Hippocampal aggregation signatures of pathogenic UBQLN2 in amyotrophic lateral sclerosis and frontotemporal dementia.

Pathogenic variants in the UBQLN2 gene cause X-linked dominant amyotrophic lateral sclerosis and/or frontotemporal dementia characterised by ubiquilin 2 aggregates in neurons of the motor cortex, hippocampus, and spinal cord. However, ubiquilin 2 neuropathology is also seen in sporadic and familial amyotrophic lateral sclerosis and/or frontotemporal dementia cases not caused by UBQLN2 pathogenic variants, particularly C9orf72-linked cases. This makes the mechanistic role of mutant ubiquilin 2 protein and the value of ubiquilin 2 pathology for predicting genotype unclear. Here we examine a cohort of 44 genotypically diverse amyotrophic lateral sclerosis cases with or without frontotemporal dementia, including eight cases with UBQLN2 variants (resulting in p.S222G, p.P497H, p.P506S, p.T487I (two cases), and p.P497L (three cases)). Using multiplexed (5-label) fluorescent immunohistochemistry, we mapped the co-localisation of ubiquilin 2 with phosphorylated TDP-43, dipeptide repeat aggregates, and p62, in the hippocampus of controls (n = 6), or amyotrophic lateral sclerosis with or without frontotemporal dementia in sporadic (n = 20), unknown familial (n = 3), SOD1-linked (n = 1), FUS-linked (n = 1), C9orf72-linked (n = 5), and UBQLN2-linked (n = 8) cases. We differentiate between i) ubiquilin 2 aggregation together with phosphorylated TDP-43 or dipeptide repeat proteins, and ii) ubiquilin 2 self-aggregation promoted by UBQLN2 pathogenic variants that cause amyotrophic lateral sclerosis/and frontotemporal dementia. Overall, we describe a hippocampal protein aggregation signature that fully distinguishes mutant from wildtype ubiquilin 2 in amyotrophic lateral sclerosis with or without frontotemporal dementia, whereby mutant ubiquilin 2 is more prone than wildtype to aggregate independently of driving factors. This neuropathological signature can be used to assess the pathogenicity of UBQLN2 gene variants and to understand the mechanisms of UBQLN2-linked disease.

Inflammatory plasma profile in genetic symptomatic and presymptomatic Frontotemporal Dementia - A GENFI study.

BACKGROUND: Inflammation has been proposed as a crucial player in neurodegeneration, including Frontotemporal Dementia (FTD). A few studies on sporadic FTD lead to inconclusive results, whereas large studies on genetic FTD are lacking. The aim of this study is to determine cytokine and chemokine plasma circulating levels in a large cohort of genetic FTD, collected within the GENetic Frontotemporal dementia Initiative (GENFI). METHODS: Mesoscale technology was used to analyse levels of 30 inflammatory factors in 434 plasma samples, including 94 Symptomatic Mutation carriers [(SMC); 15 with mutations in Microtubule Associated Protein Tau (MAPT) 34 in Progranulin (GRN) and 45 in Chromosome 9 Open Reading Frame (C9ORF)72], 168 Presymptomatic Mutation Carriers (PMC; 34 MAPT, 70 GRN and 64 C9ORF72) and 173 Non-carrier Controls (NC)]. RESULTS: The following cytokines were significantly upregulated (P<0.05) in MAPT and GRN SMC versus NC: Tumor Necrosis Factor (TNF)α, Interleukin (IL)-7, IL-15, IL-16, IL-17A. Moreover, only in GRN SMC, additional factors were upregulated, including: IL-1ß, IL-6, IL-10, IL-12/IL-23p40, eotaxin, eotaxin-3, Interferon γ-induced Protein (IP-10), Monocyte Chemotactic Protein (MCP)4. On the contrary, IL-1α levels were decreased in SMC compared with NC. Significantly decreased levels of this cytokine were also found in PMC, independent of the type of mutation. In SMC, no correlations between disease duration and cytokine and chemokine levels were found. Considering NfL and GFAP levels, as expected, significant increases were observed in SMC as compared to NC. These differences in mean values remain significant even when stratifying symptomatic patients by the mutated gene (P<0.0001). Considering instead the levels of NfL, GFAP, and the altered inflammatory molecules, no significant correlations emerged. CONCLUSION: We showed that inflammatory proteins are upregulated in MAPT and GRN SMC, with some specific factors altered in GRN only, whereas no changes were seen in C9ORF72 carriers. Notably, only IL-1α levels were decreased in both SMC and PMC, independent of the type of causal mutation, suggesting common modifications occurring in the preclinical phase of the disease.

Cerebrospinal fluid and blood neurofilament light chain levels in amyotrophic lateral sclerosis and frontotemporal degeneration: A meta-analysis.

BACKGROUND AND PURPOSE: Neurofilament light chain (NFL) has been shown to be increased in amyotrophic lateral sclerosis (ALS) and, to a lesser extent, in frontotemporal dementia (FTD). A meta-analysis of NFL in ALS and FTD was performed. METHODS: Available studies comparing cerebrospinal fluid and blood NFL levels in ALS versus neurologically healthy controls (NHCs), other neurological diseases (ONDs) and ALS mimics, as well as in FTD and related entities (behavioural variant of FTD and frontotemporal lobar degeneration syndromes) versus NHCs, ONDs and other dementias were evaluated. RESULTS: In ALS, both cerebrospinal fluid and blood levels of NFL were higher compared to other categories. In FTD, behavioural variant of FTD and frontotemporal lobar degeneration syndromes, NFL levels were consistently higher compared to NHCs; however, several comparisons with ONDs and other dementias did not demonstrate significant differences. DISCUSSION: Amyotrophic lateral sclerosis is characterized by higher NFL levels compared to most other conditions. In contrast, NFL is not as good at discriminating FTD from other dementias.

Frontotemporal lobar degeneration in the "Annual of the Pathological Autopsy Cases in Japan".

BACKGROUND: Good accuracy for the clinical diagnosis of frontotemporal lobar degeneration (FTLD) by specialists in an early onset dementia clinic has been reported. OBJECTIVE: To assess the diagnostic accuracy of FTLD in an entire population, without restrictions related to patient age or diagnosing physician. METHODS: Volumes of the "Annual of the Pathological Autopsy Cases in Japan," with reports of 130,105 autopsies throughout Japan from 2007 to 2016, were descriptively analyzed. RESULTS: There were 219 patients with clinical and/or pathological diagnoses of FTLD. The sensitivity and specificity were 24.5% and 76.9%, respectively. Age at death for pathologically confirmed patients was 76.3 ± 11.6 years (mean ± standard deviation). Overlooked patients died significantly older than patients with an accurate clinical diagnosis. CONCLUSIONS: Clinical diagnoses of FTLD had low sensitivity. Furthermore, the age at death of pathologically confirmed patients suggests that FTLD affects a wide age range and is not restricted to presenile individuals.

Distribution of ubiquilin 2 and TDP-43 aggregates throughout the CNS in UBQLN2 p.T487I-linked amyotrophic lateral sclerosis and frontotemporal dementia.

Mutations in the UBQLN2 gene cause amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). The neuropathology of such UBQLN2-linked cases of ALS/FTD is characterised by aggregates of the ubiquilin 2 protein in addition to aggregates of the transactive response DNA-binding protein of 43 kDa (TDP-43). ALS and FTD without UBQLN2 mutations are also characterised by TDP-43 aggregates, that may or may not colocalise with wildtype ubiquilin 2. Despite this, the relative contributions of TDP-43 and ubiquilin 2 to disease pathogenesis remain largely under-characterised, as does their relative deposition as aggregates across the central nervous system (CNS). Here we conducted multiplex immunohistochemistry of three UBQLN2 p.T487I-linked ALS/FTD cases, three non-UBQLN2-linked (sporadic) ALS cases, and 8 non-neurodegenerative disease controls, covering 40 CNS regions. We then quantified ubiquilin 2 aggregates, TDP-43 aggregates and aggregates containing both proteins in regions of interest to determine how UBQLN2-linked and non-UBQLN2-linked proteinopathy differ. We find that ubiquilin 2 aggregates that are negative for TDP-43 are predominantly small and punctate and are abundant in the hippocampal formation, spinal cord, all tested regions of neocortex, medulla and substantia nigra in UBQLN2-linked ALS/FTD but not sporadic ALS. Curiously, the striatum harboured small punctate ubiquilin 2 aggregates in all cases examined, while large diffuse striatal ubiquilin 2 aggregates were specific to UBQLN2-linked ALS/FTD. Overall, ubiquilin 2 is mainly deposited in clinically unaffected regions throughout the CNS such that symptomology in UBQLN2-linked cases maps best to the aggregation of TDP-43.

Flight to insight: maximizing the potential of Drosophila models of C9orf72-FTD.

Advancements in understanding the pathogenesis of C9orf72-associated frontotemporal dementia (C9orf72-FTD) have highlighted the role of repeat-associated non-ATG (RAN) translation and dipeptide repeat proteins (DPRs), with Drosophila melanogaster models providing valuable insights. While studies have primarily focused on RAN translation and DPR toxicity, emerging areas of investigation in fly models have expanded to neuronal dysfunction, autophagy impairment, and synaptic dysfunction, providing potential directions for new therapeutic targets and mechanisms of neurodegeneration. Despite this progress, there are still significant gaps in Drosophila models of C9orf72-FTD, namely in the areas of metabolism and circadian rhythm. Metabolic dysregulation, particularly lipid metabolism, autophagy, and insulin signaling, has been implicated in disease progression with findings from animal models and human patients with C9orf72 repeat expansions. Moreover, circadian disruptions have been observed in C9of72-FTD, with alterations in rest-activity patterns and cellular circadian machinery, suggesting a potential role in disease pathophysiology. Drosophila models offer unique opportunities to explore these aspects of C9orf72-FTD and identify novel therapeutic targets aimed at mitigating neurodegeneration.

Traumatic injury causes selective degeneration and TDP-43 mislocalization in human iPSC-derived C9orf72-associated ALS/FTD motor neurons.

A hexanucleotide repeat expansion (HRE) in C9orf72 is the most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). However, patients with the HRE exhibit a wide disparity in clinical presentation and age of symptom onset suggesting an interplay between genetic background and environmental stressors. Neurotrauma as a result of traumatic brain or spinal cord injury has been shown to increase the risk of ALS/FTD in epidemiological studies. Here, we combine patient-specific induced pluripotent stem cells (iPSCs) with a custom-built device to deliver biofidelic stretch trauma to C9orf72 patient and isogenic control motor neurons (MNs) in vitro. We find that mutant but not control MNs exhibit selective degeneration after a single incident of severe trauma, which can be partially rescued by pretreatment with a C9orf72 antisense oligonucleotide. A single incident of mild trauma does not cause degeneration but leads to cytoplasmic accumulation of TDP-43 in C9orf72 MNs. This mislocalization, which only occurs briefly in isogenic controls, is eventually restored in C9orf72 MNs after 6 days. Lastly, repeated mild trauma ablates the ability of patient MNs to recover. These findings highlight alterations in TDP-43 dynamics in C9orf72 ALS/FTD patient MNs following traumatic injury and demonstrate that neurotrauma compounds neuropathology in C9orf72 ALS/FTD. More broadly, our work establishes an in vitro platform that can be used to interrogate the mechanistic interactions between ALS/FTD and neurotrauma.

A complex network of interdomain interactions underlies the conformational ensemble of monomeric TDP-43 and modulates its phase behavior.

TAR DNA-binding protein 43 (TDP-43) is a multidomain protein involved in the regulation of RNA metabolism, and its aggregates have been observed in neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Numerous studies indicate TDP-43 can undergo liquid-liquid phase separation (LLPS) in vitro and is a component of biological condensates. Homo-oligomerization via the folded N-terminal domain (aa:1-77) and the conserved helical region (aa:319-341) of the disordered, C-terminal domain is found to be an important driver of TDP-43 phase separation. However, a comprehensive molecular view of TDP-43 phase separation, particularly regarding the nature of heterodomain interactions, is lacking due to the challenges associated with its stability and purification. Here, we utilize all-atom and coarse-grained (CG) molecular dynamics (MD) simulations to uncover the network of interdomain interactions implicated in TDP-43 phase separation. All-atom simulations uncovered the presence of transient, interdomain interactions involving flexible linkers, RNA-recognition motif (RRM) domains and a charged segment of disordered C-terminal domain (CTD). CG simulations indicate these inter-domain interactions which affect the conformational landscape of TDP-43 in the dilute phase are also prevalent in the condensed phase. Finally, sequence and surface charge distribution analysis coupled with all-atom simulations (at high salt) confirmed that the transient interdomain contacts are predominantly electrostatic in nature. Overall, our findings from multiscale simulations lead to a greater appreciation of the complex interaction network underlying the structural landscape and phase separation of TDP-43.

Cytoplasmic Accumulation of Histones Induced by BET Inhibition Protects Cells from C9orf72 Poly(PR)-Induced Cell Death.

Repeat dipeptides such as poly(proline-arginine) (polyPR) are generated from the hexanucleotide GGGGCC repeat expansions in the C9orf72 gene. These dipeptides are often considered as the genetic cause of familial amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). In the study, fluorescein isothiocyanate (FITC) labeled PR20 is used to investigate PR20-induced cell death. The findings reveal that the cell death induced by PR20 is dependent on its nuclear distribution and can be blocked by a nuclear import inhibitor called importazole. Further investigation reveals that BRD4 inhibitors, such as JQ-1 and I-BET762, restrict cytoplasmic localization of PR20, thereby reducing its cytotoxic effect. Mechanistically, the inhibition of BRD4 leads to an increase in the expression of numerous histones, resulting in the accumulation of histones in the cytoplasm. These cytoplasmic histones associate with PR20 and limit its distribution within the nucleus. Notably, the ectopic expression of histones alone is enough to confer protection to cells treated with PR20. In addition, phenylephrine (PE) induces cellular hypertrophy and cytoplasmic distribution of histone, which also helps protect cells from PR20-induced cell death. The research suggests that temporarily inducing the presence of cytoplasmic histones may alleviate the neurotoxic effects of dipeptide repeat proteins.

Frontotemporal dementia: from genetics to therapeutic approaches.

INTRODUCTION: Frontotemporal dementia (FTD) includes a group of neurodegenerative diseases characterized clinically by behavioral disturbances and by neurodegeneration of brain anterior temporal and frontal lobes, leading to atrophy. Apart from symptomatic treatments, there is, at present, no disease-modifying cure for FTD. AREAS COVERED: Three main mutations are known as causes of familial FTD, and large consortia have studied carriers of mutations, also in preclinical Phases. As genetic cases are the only ones in which the pathology can be predicted in life, compounds developed so far are directed toward specific proteins or mutations. Herein, recently approved clinical trials will be summarized, including molecules, mechanisms of action and pharmacological testing. EXPERT OPINION: These studies are paving the way for the future. They will clarify whether single mutations should be addressed rather than common proteins depositing in the brain to move from genetic to sporadic FTD.