TAR DNA-binding Protein Research Articles

Studies of Genetic and Proteomic Risk Factors of Amyotrophic Lateral Sclerosis Inspire Biomarker Development and Gene Therapy.

Amyotrophic lateral sclerosis (ALS) is an incurable neurodegenerative disease affecting the upper and lower motor neurons, leading to muscle weakness, motor impairments, disabilities and death. Approximately 5-10% of ALS cases are associated with positive family history (familial ALS or fALS), whilst the remainder are sporadic (sporadic ALS, sALS). At least 50 genes have been identified as causative or risk factors for ALS. Established pathogenic variants include superoxide dismutase type 1 (SOD1), chromosome 9 open reading frame 72 (c9orf72), TAR DNA Binding Protein (TARDBP), and Fused In Sarcoma (FUS); additional ALS-related genes including Charged Multivesicular Body Protein 2B (CHMP2B), Senataxin (SETX), Sequestosome 1 (SQSTM1), TANK Binding Kinase 1 (TBK1) and NIMA Related Kinase 1 (NEK1), have been identified. Mutations in these genes could impair different mechanisms, including vesicle transport, autophagy, and cytoskeletal or mitochondrial functions. So far, there is no effective therapy against ALS. Thus, early diagnosis and disease risk predictions remain one of the best options against ALS symptomologies. Proteomic biomarkers, microRNAs, and extracellular vehicles (EVs) serve as promising tools for disease diagnosis or progression assessment. These markers are relatively easy to obtain from blood or cerebrospinal fluids and can be used to identify potential genetic causative and risk factors even in the preclinical stage before symptoms appear. In addition, antisense oligonucleotides and RNA gene therapies have successfully been employed against other diseases, such as childhood-onset spinal muscular atrophy (SMA), which could also give hope to ALS patients. Therefore, an effective gene and biomarker panel should be generated for potentially "at risk" individuals to provide timely interventions and better treatment outcomes for ALS patients as soon as possible.

A Novel Drosophila-based Drug Repurposing Platform Identified Fingolimod As a Potential Therapeutic for TDP-43 Proteinopathy.

Pathogenic changes to TAR DNA-binding protein 43 (TDP-43) leading to alteration of its homeostasis are a common feature shared by several progressive neurodegenerative diseases for which there is no effective therapy. Here, we developed Drosophila lines expressing either wild type TDP-43 (WT) or that carrying an Amyotrophic Lateral Sclerosis /Frontotemporal Lobar Degeneration-associating G384C mutation that recapitulate several aspects of the TDP-43 pathology. To identify potential therapeutics for TDP-43-related diseases, we implemented a drug repurposing strategy that involved three consecutive steps. Firstly, we evaluated the improvement of eclosion rate, followed by the assessment of locomotive functions at early and late developmental stages. Through this approach, we successfully identified fingolimod, as a promising candidate for modulating TDP-43 toxicity. Fingolimod exhibited several beneficial effects in both WT and mutant models of TDP-43 pathology, including post-transcriptional reduction of TDP-43 levels, rescue of pupal lethality, and improvement of locomotor dysfunctions. These findings provide compelling evidence for the therapeutic potential of fingolimod in addressing TDP-43 pathology, thereby strengthening the rationale for further investigation and consideration of clinical trials. Furthermore, our study demonstrates the utility of our Drosophila-based screening pipeline in identifying novel therapeutics for TDP-43-related diseases. These findings encourage further scale-up screening endeavors using this platform to discover additional compounds with therapeutic potential for TDP-43 pathology.

Specific vulnerability of iPSC-derived motor neurons with TDP-43 gene mutation to oxidative stress

Amyotrophic lateral sclerosis (ALS) is a disease that affects motor neurons and has a poor prognosis. We focused on TAR DNA-binding protein 43 kDa (TDP-43), which is a common component of neuronal inclusions in many ALS patients. To analyze the contribution of TDP-43 mutations to ALS in human cells, we first introduced TDP-43 mutations into healthy human iPSCs using CRISPR/Cas9 gene editing technology, induced the differentiation of these cells into motor and sensory neurons, and analyzed factors that are assumed to be altered in or associated with ALS (cell morphology, TDP-43 localization and aggregate formation, cell death, TDP-43 splicing function, etc.). We aimed to clarify the pathological alterations caused solely by TDP-43 mutation, i.e., the changes in human iPSC-derived neurons with TDP-43 mutation compared with those with the same genetic background except TDP-43 mutation. Oxidative stress induced by hydrogen peroxide administration caused the death of TDP-43 mutant-expressing motor neurons but not in sensory neurons, indicating the specific vulnerability of human iPSC-derived motor neurons with TDP-43 mutation to oxidative stress. In our model, we observed aggregate formation in a small fraction of TDP-43 mutant-expressing motor neurons, suggesting that aggregate formation seems to be related to ALS pathology but not the direct cause of cell death. This study provides basic knowledge for elucidating the pathogenesis of ALS and developing treatments for the disease.

Astrocytic response mediated by the CLU risk allele inhibits OPC proliferation and myelination in a human iPSC model

The C allele of rs11136000 variant in the clusterin (CLU) gene represents the third strongest known genetic risk factor for late-onset Alzheimer's disease. However, whether this single-nucleotide polymorphism (SNP) is functional and what the underlying mechanisms are remain unclear. In this study, the CLU rs11136000 SNP is identified as a functional variant by a small-scale CRISPR-Cas9 screen. Astrocytes derived from isogenic induced pluripotent stem cells (iPSCs) carrying the "C" or "T" allele of the CLU rs11136000 SNP exhibit different CLU expression levels. TAR DNA-binding protein-43 (TDP-43) preferentially binds to the "C" allele to promote CLU expression and exacerbate inflammation. The interferon response and CXCL10 expression are elevated in cytokine-treated C/C astrocytes, leading to inhibition of oligodendrocyte progenitor cell (OPC) proliferation and myelination. Accordingly, elevated CLU and CXCL10 but reduced myelin basic protein (MBP) expression are detected in human brains of C/C carriers. Our study uncovers amechanism underlying reduced white matter integrity observed in the CLU rs11136000 risk "C" allele carriers.

Neuroimmune characterization of optineurin insufficiency mouse model during ageing

Optineurin is a multifunctional polyubiquitin-binding protein implicated in inflammatory signalling. Optineurin mutations are associated with amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), neurodegenerative diseases characterised by neuronal loss, neuroinflammation, and peripheral immune disbalance. However, the pathogenic role of optineurin mutations is unclear. We previously observed no phenotype in the unmanipulated young optineurin insufficiency mice (Optn470T), designed to mimic ALS/FTD-linked truncations deficient in polyubiquitin binding. The purpose of this study was to investigate whether ageing would trigger neurodegeneration. We performed a neurological, neuropathological, and immunological characterization of ageing wild-type (WT) and Optn470T mice. No motor or cognitive differences were detected between the genotypes. Neuropathological analyses demonstrated signs of ageing including lipofuscin accumulation and microglial activation in WT mice. However, this was not worsened in Optn470T mice, and they did not exhibit TAR DNA-binding protein 43 (TDP-43) aggregation or neuronal loss. Spleen immunophenotyping uncovered T cell immunosenescence at two years but without notable differences between the WT and Optn470T mice. Conventional dendritic cells (cDC) and macrophages exhibited increased expression of activation markers in two-year-old Optn470T males but not females, although the numbers of innate immune cells were similar between genotypes. Altogether, a combination of optineurin insufficiency and ageing did not induce ALS/FTD-like immune imbalance and neuropathology in mice.

Cryptic exon detection and transcriptomic changes revealed in single-nuclei RNA sequencing of C9ORF72 patients spanning the ALS-FTD spectrum

The C9ORF72-linked diseases amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are characterized by the nuclear depletion and cytoplasmic accumulation of TAR DNA-binding protein 43 (TDP-43). Recent studies have shown that the loss of TDP-43 function leads to the inclusion of cryptic exons (CE) in several RNA transcript targets of TDP-43. Here, we show for the first time the detection of CEs in a single-nuclei RNA sequencing (snRNA-seq) dataset obtained from frontal and occipital cortices of C9ORF72 patients that phenotypically span the ALS-FTD disease spectrum. We assessed each cellular cluster for detection of recently described TDP-43-induced CEs. Transcripts containing CEs in the genes STMN2 and KALRN were detected in the frontal cortex of all C9ORF72 disease groups with the highest frequency in excitatory neurons in the C9ORF72-FTD group. Within the excitatory neurons, the cluster with the highest proportion of cells containing a CE had transcriptomic similarities to von Economo neurons, which are known to be vulnerable to TDP-43 pathology and selectively lost in C9ORF72-FTD. Differential gene expression and pathway analysis of CE-containing neurons revealed multiple dysregulated metabolic processes. Our findings reveal novel insights into the transcriptomic changes of neurons vulnerable to TDP-43 pathology.

Maternal TDP-43 interacts with RNA Pol II and regulates zygotic genome activation

Zygotic genome activation (ZGA) is essential for early embryonic development. However, the regulation of ZGA remains elusive in mammals. Here we report that a maternal factor TDP-43, a nuclear transactive response DNA-binding protein, regulates ZGA through RNA Pol II and is essential for mouse early embryogenesis. Maternal TDP-43 translocates from the cytoplasm into the nucleus at the early two-cell stage when minor to major ZGA transition occurs. Genetic deletion of maternal TDP-43 results in mouse early embryos arrested at the two-cell stage. TDP-43 co-occupies with RNA Pol II as large foci in the nucleus and also at the promoters of ZGA genes at the late two-cell stage. Biochemical evidence indicates that TDP-43 binds Polr2a and Cyclin T1. Depletion of maternal TDP-43 caused the loss of Pol II foci and reduced Pol II binding on chromatin at major ZGA genes, accompanied by defective ZGA. Collectively, our results suggest that maternal TDP-43 is critical for mouse early embryonic development, in part through facilitating the correct RNA Pol II configuration and zygotic genome activation.

Different Chronic Stress Paradigms Converge on Endogenous TDP43 Cleavage and Aggregation

The TAR-DNA binding protein (TDP43) is a nuclear protein whose cytoplasmic inclusions are hallmarks of Amyotrophic Lateral Sclerosis (ALS). Acute stress in cells causes TDP43 mobilization to the cytoplasm and its aggregation through different routes. Although acute stress elicits a strong phenotype, is far from recapitulating the years-long aggregation process. We applied different chronic stress protocols and described TDP43 aggregation in a human neuroblastoma cell line by combining solubility assays, thioflavin-based microscopy and flow cytometry. This approach allowed us to detect, for the first time to our knowledge in vitro, the formation of 25 kDa C-terminal fragment of TDP43, a pathogenic hallmark of ALS. Our results indicate that chronic stress, compared to the more common acute stress paradigm, better recapitulates the cell biology of TDP43 proteinopathies. Moreover, we optimized a protocol for the detection of bona fide prions in living cells, suggesting that TDP43 may form amyloids as a stress response.

Loss of TDP‐43 oligomerization or RNA binding elicits distinct aggregation patterns

Aggregation of the RNA‐binding protein TAR DNA‐binding protein 43 (TDP‐43) is the key neuropathological feature of neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD). In physiological conditions, TDP‐43 is predominantly nuclear, forms oligomers, and is contained in biomolecular condensates assembled by liquid–liquid phase separation (LLPS). In disease, TDP‐43 forms cytoplasmic or intranuclear inclusions. How TDP‐43 transitions from physiological to pathological states remains poorly understood. Using a variety of cellular systems to express structure‐based TDP‐43 variants, including human neurons and cell lines with near‐physiological expression levels, we show that oligomerization and RNA binding govern TDP‐43 stability, splicing functionality, LLPS, and subcellular localization. Importantly, our data reveal that TDP‐43 oligomerization is modulated by RNA binding. By mimicking the impaired proteasomal activity observed in ALS/FTLD patients, we found that monomeric TDP‐43 forms inclusions in the cytoplasm, whereas its RNA binding‐deficient counterpart aggregated in the nucleus. These differentially localized aggregates emerged via distinct pathways: LLPS‐driven aggregation in the nucleus and aggresome‐dependent inclusion formation in the cytoplasm. Therefore, our work unravels the origins of heterogeneous pathological species reminiscent of those occurring in TDP‐43 proteinopathy patients.

Transactive response DNA-binding protein 43 is enriched at the centrosome in human cells.

The centrosome, as the main microtubule organizing centre, plays key roles in cell polarity, genome stability and ciliogenesis. The recent identification of ribosomes, RNA-binding proteins and transcripts at the centrosome suggests local protein synthesis. In this context, we hypothesized that TDP-43, a highly conserved RNA binding protein involved in the pathophysiology of amyotrophic lateral sclerosis and frontotemporal lobar degeneration, could be enriched at this organelle. Using dedicated high magnification sub-diffraction microscopy on human cells, we discovered a novel localization of TDP-43 at the centrosome during all phases of the cell cycle. These results were confirmed on purified centrosomes by western blot and immunofluorescence microscopy. In addition, the co-localization of TDP-43 and pericentrin suggested a pericentriolar enrichment of the protein, leading us to hypothesize that TDP-43 might interact with local mRNAs and proteins. Supporting this hypothesis, we found four conserved centrosomal mRNAs and 16 centrosomal proteins identified as direct TDP-43 interactors. More strikingly, all the 16 proteins are implicated in the pathophysiology of TDP-43 proteinopathies, suggesting that TDP-43 dysfunction in this organelle contributes to neurodegeneration. This first description of TDP-43 centrosomal enrichment paves the way for a more comprehensive understanding of TDP-43 physiology and pathology.

The identification of high-performing antibodies for TDP-43 for use in Western Blot, immunoprecipitation and immunofluorescence.

TAR DNA-binding protein 43 (TDP-43) is a DNA/RNA binding protein playing a critical role in the regulation of transcription, splicing and RNA stability. Mutations in TARDBP leading to aggregation, are suspected to be a characteristic feature of various neurogenerative diseases. The lack of well-characterized anti- TDP-43 antibodies acts as a barrier to establish reproducible TDP-43 research. In this study, we characterized eighteen TDP-43 commercial antibodies for Western blot, immunoprecipitation, and immunofluorescence using a standardized experimental protocol based on comparing read-outs in knockout cell lines and isogenic parental controls. We identified many well-performing antibodies and encourage readers to use this report as a guide to select the most appropriate antibody for their specific needs.

Machine learning approaches based on fibroblast morphometry do not predict ALS

Amyotrophic lateral sclerosis (ALS) is a devastating neuromuscular disease with limited therapeutic options. Biomarkers are needed for early disease detection, clinical trial design, and personalized medicine. Early evidence suggests that specific morphometric features in ALS primary skin fibroblasts may be used as biomarkers; however, this hypothesis has not been rigorously tested in conclusively large fibroblast populations. Here, we imaged ALS-relevant organelles (mitochondria, endoplasmic reticulum, lysosomes) and proteins (TAR DNA-binding protein 43, Ras GTPase-activating protein-binding protein 1, heat-shock protein 60) at baseline and under stress perturbations and tested their predictive power on a total set of 443 human fibroblast lines from ALS and healthy individuals. Machine learning approaches were able to confidently predict stress perturbation states (ROC-AUC ∼0.99) but not disease groups or clinical features (ROC-AUC 0.58–0.64). Our findings indicate that multivariate models using patient-derived fibroblast morphometry can accurately predict different stressors but are insufficient to develop viable ALS biomarkers.

Rare exonic variant affects GRN splicing and contributes to frontotemporal lobar degeneration

Heterozygous loss-of-function (LOF) mutations in the progranulin gene (GRN) cause frontotemporal lobar degeneration (FTLD) by a mechanism of haploinsufficiency. For most missense mutations, the contribution to FTLD is however unclear. We studied the pathogenicity of rare GRN missense mutations using patient biomaterials. We identified a new mutation in GRN, c.1178 A>C, in a patient with a diagnosis of primary progressive aphasia. Neuropathological examination of autopsied brain showed FTLD with TAR DNA-binding protein 43 (FTLD-TDP) type A pathology with concomitant Alzheimer’s disease pathology. Serum progranulin protein levels were reduced to levels comparable to known LOF mutations. The mutation is in the last codon of exon 10, in the splice donor sequence. Our data provide evidence that the mutation leads to aberrant splicing, resulting in a frameshift (p.(Glu393AlafsTer31)) and consequently nonsense-mediated mRNA decay. Our finding demonstrates that carefully examining sequencing data around splice sites is needed since this mutation was annotated as a missense mutation. Unraveling the pathogenicity of variants of unknown significance is important for clinical diagnosis and genetic counseling.

HnRNP Pathologies in Frontotemporal Lobar Degeneration

Frontotemporal dementia (FTD) is the second most common form of young-onset (<65 years) dementia. Clinically, it primarily manifests as a disorder of behavioural, executive, and/or language functions. Pathologically, frontotemporal lobar degeneration (FTLD) is the predominant cause of FTD. FTLD is a proteinopathy, and the main pathological proteins identified so far are tau, TAR DNA-binding protein 43 (TDP-43), and fused in sarcoma (FUS). As TDP-43 and FUS are members of the heterogeneous ribonucleic acid protein (hnRNP) family, many studies in recent years have expanded the research on the relationship between other hnRNPs and FTLD pathology. Indeed, these studies provide evidence for an association between hnRNP abnormalities and FTLD. In particular, several studies have shown that multiple hnRNPs may exhibit nuclear depletion and cytoplasmic mislocalisation within neurons in FTLD cases. However, due to the diversity and complex association of hnRNPs, most studies are still at the stage of histological discovery of different hnRNP abnormalities in FTLD. We herein review the latest studies relating hnRNPs to FTLD. Together, these studies outline an important role of multiple hnRNPs in the pathogenesis of FTLD and suggest that future research into FTLD should include the whole spectrum of this protein family.

Comparison of Clinical, Genetic, and Pathologic Features of Limbic and Diffuse Transactive Response DNA-Binding Protein 43 Pathology in Alzheimer's Disease Neuropathologic Spectrum.

Increasing evidence suggests that TAR DNA-binding protein 43 (TDP-43) pathology in Alzheimer's disease (AD), or AD-TDP, can be diffuse or limbic-predominant. Understanding whether diffuse AD-TDP has genetic, clinical, and pathological features that differ from limbic AD-TDP could have clinical and research implications. To better characterize the clinical and pathologic features of diffuse AD-TDP and differentiate it from limbic AD-TDP. 363 participants from the Mayo Clinic Study of Aging, Alzheimer's Disease Research Center, and Neurodegenerative Research Group with autopsy confirmed AD and TDP-43 pathology were included. All underwent genetic, clinical, neuropsychologic, and neuropathologic evaluations. AD-TDP pathology distribution was assessed using the Josephs 6-stage scale. Stages 1-3 were classified as Limbic, those 4-6 as Diffuse. Multivariable logistic regression was used to identify clinicopathologic features that independently predicted diffuse pathology. The cohort was 61% female and old at onset (median: 76 years [IQR:70-82]) and death (median: 88 years [IQR:82-92]). Fifty-four percent were Limbic and 46% Diffuse. Clinically, ∼10-20% increases in odds of being Diffuse associated with 5-year increments in age at onset (p = 0.04), 1-year longer disease duration (p = 0.02), and higher Neuropsychiatric Inventory scores (p = 0.03), while 15-second longer Trailmaking Test-B times (p = 0.02) and higher Block Design Test scores (p = 0.02) independently decreased the odds by ~10-15%. There was evidence for association of APOEɛ4 allele with limbic AD-TDP and of TMEM106B rs3173615 C allele with diffuse AD-TDP. Pathologically, widespread amyloid-β plaques (Thal phases: 3-5) decreased the odds of diffuse TDP-43 pathology by 80-90%, while hippocampal sclerosis increased it sixfold (p < 0.001). Diffuse AD-TDP shows clinicopathologic and genetic features different from limbic AD-TDP.

Loss of TDP-43 causes ectopic endothelial sprouting and migration defects through increased fibronectin, vcam 1 and integrin α4/β1.

Aggregation of the Tar DNA-binding protein of 43kDa (TDP-43) is a pathological hallmark of amyotrophic lateral sclerosis and frontotemporal dementia and likely contributes to disease by loss of nuclear function. Analysis of TDP-43 function in knockout zebrafish identified an endothelial directional migration and hypersprouting phenotype during development prior lethality. In human umbilical vein cells (HUVEC) the loss of TDP-43 leads to hyperbranching. We identified elevated expression of FIBRONECTIN 1 (FN1), the VASCULAR CELL ADHESION MOLECULE 1 (VCAM1), as well as their receptor INTEGRIN α4β1 (ITGA4B1) in HUVEC cells. Importantly, reducing the levels of ITGA4, FN1, and VCAM1 homologues in the TDP-43 loss-of-function zebrafish rescues the angiogenic defects indicating the conservation of human and zebrafish TDP-43 function during angiogenesis. Our study identifies a novel pathway regulated by TDP-43 important for angiogenesis during development.

Clinicoradiologic and Neuropathologic Evaluation of Corticobasal Syndrome.

Corticobasal syndrome (CBS) is a clinical phenotype characterized by asymmetric parkinsonism, rigidity, myoclonus, and apraxia. Originally believed secondary to corticobasal degeneration (CBD), mounting clinicopathologic studies have revealed heterogenous neuropathologies. The objectives of this study were to determine the pathologic heterogeneity of CBS, the clinicoradiologic findings associated with different underlying pathologies causing CBS, and the positive predictive value (PPV) of current diagnostic criteria for CBD among patients with a CBS. Clinical data, brain MRI, and neuropathologic data of patients followed at Mayo Clinic and diagnosed with CBS antemortem were reviewed according to neuropathology category at autopsy. The cohort consisted of 113 patients with CBS, 61 (54%) female patients. Mean ± SD disease duration was 7 ± 3.7 years; mean ± SD age at death was 70.5 ± 9.1 years. The primary neuropathologic diagnoses were 43 (38%) CBD, 27 (24%) progressive supranuclear palsy (PSP), 17 (15%) Alzheimer disease (AD), 10 (9%) frontotemporal lobar degeneration (FTLD) with TAR DNA-binding protein 43 (TDP) inclusions, 7 (6%) diffuse Lewy body disease (DLBD)/AD, and 9 (8%) with other diagnoses. Patients with CBS-AD or CBS-DLBD/AD were youngest at death (median [interquartile range]: 64 [13], 64 [11] years) while CBS-PSP were oldest (77 [12.5] years, p = 0.024). Patients with CBS-DLBD/AD had the longest disease duration (9 [6] years), while CBS-other had the shortest (3 [4.25] years, p = 0.04). Posterior cortical signs and myoclonus were more characteristic of patients with CBS-AD and patients with CBS-DLBD/AD. Patients with CBS-DLBD/AD displayed more features of Lewy body dementia. Voxel-based morphometry revealed widespread cortical gray matter loss characteristic of CBS-AD, while CBS-CBD and CBS-PSP predominantly involved premotor regions with greater amount of white matter loss. Patients with CBS-DLBD/AD showed atrophy in a focal parieto-occipital region, and patients with CBS-FTLD-TDP had predominant prefrontal cortical loss. Patients with CBS-PSP had the lowest midbrain/pons ratio (p = 0.012). Of 67 cases meeting clinical criteria for possible CBD at presentation, 27 were pathology-proven CBD, yielding a PPV of 40%. A variety of neurodegenerative disorders can be identified in patients with CBS, but clinical and regional imaging differences aid in predicting underlying neuropathology. PPV analysis of the current CBD diagnostic criteria revealed suboptimal performance. Biomarkers adequately sensitive and specific for CBD are needed.

Retinal TDP43 pathology in Alzheimer’s disease, Parkinson’s disease and frontotemporal dementia

AbstractBackgroundAs an extension of the brain, the retina displays similarities with the brain in terms of anatomy and functionality. The accessibility of the retina provides a ‘window’ to the brain and a great potential for noninvasive imaging of neurodegenerative changes in patients. TAR DNA binding protein 43 (TDP‐43) is one of the main pathological hallmarks found in frontotemporal lobar degeneration (FTLD). Previously, we identified phosphorylated TDP‐43 (pTDP‐43) aggregation in the retina of FTLD cases with underlying TDP43 (FTLD‐TDP) pathology, including donors with C9orf72 and progranulin (GRN) mutations. The aim of this study is to assess the presence of pTDP‐43 in the retina across various neurodegenerative diseases and controls. This will provide insight in whether the presence of TDP43 pathology in the retina is exclusive for cases with FTLD‐TDP and potentially serve as an in‐vivo biomarker.MethodPost‐mortem eyes were collected by the Netherlands Brain Bank from donors with Alzheimer’s disease (AD), Parkinson’s disease (PD), frontotemporal dementia (FTD) and controls (N = 80). Nasal superior‐temporal quadrants were cut in sections of 10 µm. Immunohistochemical stainings were performed for phosphorylated TDP‐43 (pTDP‐43).ResultFTLD‐TDP cases showed pTDP‐43 immunopositive inclusions in the plexiform layers. Additionally, some AD cases showed sparse pTDP‐43 positive inclusions. Data of the other pathological groups will be available within a couple of months.ConclusionpTDP‐43 is abundantly present in the retina of FTLD‐TDP patients, while only sporadically seen in AD patients. With the advances in ocular imaging techniques, these findings provide a patient friendly retinal biomarker to diagnose FTLD‐TDP. This would be the first FTD specific biomarker, since no other pathology specific biomarkers for the various underlying pathological changes that are known to cause FTD (e.g. tau, FUS, etc), are currently available.

Utility of linguistic biomarkers for prediction of cognitive impairment and limbic predominant age related TDP‐43 neuropathologic change in the oldest old

AbstractBackgroundThere is an urgent need for accessible biomarkers that can predict cognitive impairment in older individuals. There is also a complete lack of biomarkers for TAR DNA‐binding protein‐43 (TDP‐43), a frequent and important neurodegenerative pathology in older individuals, currently referred to as Limbic‐predominant Age‐related TDP‐43 Encephalopathy‐Neuropathologic Change (LATE‐NC). Here we explored the utility of linguistic markers for prediction of future cognitive impairments and LATE‐NC.Method134 participants of the Leisure World cohort, an epidemiologic study in a California retirement community, produced written descriptions of the cookie‐theft picture from the Boston Aphasia Diagnostic Examination. All had normal cognition at the time. Samples were quantitatively analyzed for 31 linguistic markers (see table 1 for definitions of select relevant variables). Participants subsequently joined the 90+ study and underwent cognitive assessments every 6 months and autopsy after death. Cognitive impairment and its onset date were determined at postmortem conferences. LATE‐NC was considered present in those with TDP‐43 in hippocampus or neocortex, and Alzheimer’s disease neuropathologic change (ADNC) in those with high likelihood ADNC according to NIA‐ AA guidelines. To examine the relationships between linguistic markers and future cognitive impairment and presence of LATE‐NC and ADNC, we used logistic regression analysis. Models were adjusted for sex, education, age at the time of writing the samples and age at death.ResultTable 2 summarizes demographic and neuropathology findings. Additionally, mean age at cognitive impairment was 93.2 in 72% who developed cognitive impairment. Future cognitive impairment was significantly associated with less information content (OR:0.02) and fewer clauses (OR:0.93) (Table 3). Also, presence of LATE‐NC was significantly associated with higher proportions of content words (OR:7.2), higher proportion of function word errors (OR:10.5), and fewer complete units (OR:0.15). Lower number of words also trended towards a significant association (OR:8, p = 0.07) with LATE‐NC. No language measure was associated with ADNC.ConclusionOur results suggest that linguistic markers derived from writing samples obtained on average 8 years prior to development of cognitive impairment and 12 years before death might serve as biomarkers for future cognitive impairment and presence of LATE‐NC at autopsy.

Assessing neuroinflammatory differences in FTLD‐Tau vs FTLD‐TDP using free water diffusion

AbstractBackgroundFrontotemporal lobar degeneration (FTLD) is associated with two pathological substrates: Tau and TAR‐DNA‐binding protein 43 (TDP‐43). In‐vivo detection of the pathological substrate is still not possible in FTLD‐related syndromes but progressive supranuclear palsy (PSP) is consistently associated with FTLD‐Tau while semantic‐variant primary progressive aphasia (svPPA) and FTD‐MND (FTD‐ALS) are associated with FTLD‐TDP. In the absence of disease‐specific markers in FTLD, it is necessary to identify biomarkers that can help distinguish FTLD‐Tau and FTLD‐TDP. Recent research has implicated neuroinflammation as a common feature across FTLD subtypes (Bright et al., 2019), however further research is required to investigate neuroinflammatory differences between FTLD‐Tau and FTLD‐TDP, given that microglial burden and activation may differ in FTLD subtypes (Woollacott et al., 2020). The free water fraction (FW), a metric generated from diffusion MRI (dMRI) (Pasternak et al., 2009), is a non‐specific marker of neuroinflammation (Bergamino, Walsh and Stokes, 2021). We will investigate differences in FW diffusion between patients with presumed FTLD‐Tau versus FTLD‐TDP. We hypothesize that differences in neuroinflammation between FTLD‐Tau and FTLD‐TDP can be identified using the free water measure, which may infer neuroinflammatory differences.MethodFree‐water maps were generated from dMRI datasets obtained from 43 subjects: 19 with presumed FTLD‐Tau (PSP, mean age = 70), 6 with presumed FTLD‐TDP (mean age = 67, 4 svPPA, 2 FTD‐ALS), and 19 healthy controls (mean age 63). Grey matter (GM) was segmented from T1‐weighted MRIs using FSL’s ‘fast’, projected onto the diffusion MRI space, where free‐water maps were averaged across the GM. The average free water estimates from FTLD‐Tau, FTLD‐TDP and control datasets were tested for group differences using student’s t‐tests and analysis of covariance (ANCOVA), with age as a covariate.ResultsANCOVA revealed significant differences between the groups (F = 6.47, p &lt; 0.01). Post‐hoc tests showed significantly higher free‐water in FTLD‐Tau (p&lt;0.01) and FTLD‐TDP (p&lt;0.01) compared to controls. There was also higher free water in FTLD‐TDP in comparison to FTLD‐Tau, approaching significance (p = 0.0503)ConclusionOur preliminary data shows significant differences between healthy controls and patients with FTLD‐Tau and FTLD‐TDP and a trend for increased free water in FTLD‐TDP patients vs FTLD‐Tau, which may be indicative of neuroinflammatory differences.