TMEM106B modifies TDP-43 pathology in human ALS brain and cell-based models of TDP-43 proteinopathy.

The neurodegenerative diseases amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration with TAR DNA-binding protein-43 (TDP-43) inclusions (FTLD-TDP) share the neuropathological hallmark of aggregates of TDP-43. However, factors governing the severity and regional distribution of TDP-43 pathology, which may account for the divergent clinical presentations of ALS and FTLD-TDP, are not well understood. Here, we investigated the influence of genotypes at TMEM106B, a locus associated with risk for FTLD-TDP, and hexanucleotide repeat expansions in C9orf72, a known genetic cause for both ALS and FTLD-TDP, on global TDP-43 pathology and regional distribution of TDP-43 pathology in 899 postmortem cases from a spectrum of neurodegenerative diseases. We found that, among the 110 ALS cases, minor (C)-allele homozygotes at the TMEM106B locus sentinel SNP rs1990622 had more TDP-43 pathology globally, as well as in select brain regions. C9orf72 expansions similarly associated with greater TDP-43 pathology in ALS. However, adjusting for C9orf72 expansion status did not affect the relationship between TMEM106B genotype and TDP-43 pathology. To elucidate the direction of causality for this association, we directly manipulated TMEM106B levels in an inducible cell system that expresses mislocalized TDP-43 protein. We found that partial knockdown of TMEM106B, to levels similar to what would be expected in rs1990622 C allele carriers, led to development of more TDP-43 cytoplasmic aggregates, which were more insoluble, in this system. Taken together, our results support a causal role for TMEM106B in modifying the development of TDP-43 proteinopathy.

Molecular Mechanisms Underlying TDP-43 Pathology in Cellular and Animal Models of ALS and FTLD.

Amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD) are neurodegenerative disorders that exist on a disease spectrum due to pathological, clinical and genetic overlap. In up to 97% of ALS cases and ~50% of FTLD cases, the primary pathological protein observed in affected tissues is TDP-43, which is hyperphosphorylated, ubiquitinated and cleaved. The TDP-43 is observed in aggregates that are abnormally located in the cytoplasm. The pathogenicity of TDP-43 cytoplasmic aggregates may be linked with both a loss of nuclear function and a gain of toxic functions. The cellular processes involved in ALS and FTLD disease pathogenesis include changes to RNA splicing, abnormal stress granules, mitochondrial dysfunction, impairments to axonal transport and autophagy, abnormal neuromuscular junctions, endoplasmic reticulum stress and the subsequent induction of the unfolded protein response. Here, we review and discuss the evidence for alterations to these processes that have been reported in cellular and animal models of TDP-43 proteinopathy.

Hsp90 and its co-chaperone Sti1 control TDP-43 misfolding and toxicity.

Protein misfolding is a central feature of most neurodegenerative diseases. Molecular chaperones can modulate the toxicity associated with protein misfolding, but it remains elusive which molecular chaperones and co-chaperones interact with specific misfolded proteins. TDP-43 misfolding and inclusion formation are a hallmark of amyotrophic lateral sclerosis (ALS) and other neurodegenerative diseases. Using yeast and mammalian neuronal cells we find that Hsp90 and its co-chaperone Sti1 have the capacity to alter TDP-43 misfolding, inclusion formation, aggregation, and cellular toxicity. Our data also demonstrate that impaired Hsp90 function sensitizes cells to TDP-43 toxicity and that Sti1 specifically interacts with and strongly modulates TDP-43 toxicity in a dose-dependent manner. Our study thus uncovers a previously unrecognized tie between Hsp90, Sti1, TDP-43 misfolding, and cellular toxicity.

Long non-coding RNA NEAT1_1 ameliorates TDP-43 toxicity in in vivo models of TDP-43 proteinopathy.

Pathological changes involving TDP-43 protein ('TDP-43 proteinopathy') are typical for several neurodegenerative diseases, including frontotemporal lobar degeneration (FTLD). FTLD-TDP cases are characterized by increased binding of TDP-43 to an abundant lncRNA, NEAT1, in the cortex. However it is unclear whether enhanced TDP-43-NEAT1 interaction represents a protective mechanism. We show that accumulation of human TDP-43 leads to upregulation of the constitutive NEAT1 isoform, NEAT1_1, in cultured cells and in the brains of transgenic mice. Further, we demonstrate that overexpression of NEAT1_1 ameliorates TDP-43 toxicity in Drosophila and yeast models of TDP-43 proteinopathy. Thus, NEAT1_1 upregulation may be protective in TDP-43 proteinopathies affecting the brain. Approaches to boost NEAT1_1 expression in the CNS may prove useful in the treatment of these conditions.

Association of TDP-43 proteinopathy, cerebral amyloid angiopathy, and Lewy bodies with cognitive impairment in individuals with or without Alzheimer's disease neuropathology.

Alzheimer's disease patients typically present with multiple co-morbid neuropathologies at autopsy, but the impact of these pathologies on cognitive impairment during life is poorly understood. In this study, we developed cognitive trajectories for patients with common co-pathologies in the presence and absence of Alzheimer's disease neuropathology. Cognitive trajectories were modelled in a Bayesian hierarchical regression framework to estimate the effects of each neuropathology on cognitive decline as assessed by the mini-mental state examination and the clinical dementia rating scale sum of boxes scores. We show that both TDP-43 proteinopathy and cerebral amyloid angiopathy associate with cognitive impairment of similar magnitude to that associated with Alzheimer's disease neuropathology. Within our study population, 63% of individuals given the 'gold-standard' neuropathological diagnosis of Alzheimer's disease in fact possessed either TDP-43 proteinopathy or cerebral amyloid angiopathy of sufficient severity to independently explain the majority of their cognitive impairment. This suggests that many individuals diagnosed with Alzheimer's disease may actually suffer from a mixed dementia, and therapeutics targeting only Alzheimer's disease-related processes may have severely limited efficacy in these co-morbid populations.

The influence of Aß-dependent and independent pathways on TDP-43 proteinopathy in Alzheimer's disease: a possible connection to LATE-NC.

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that results from the accumulation of plaques by cleaved Aß42 peptides as well as neurofibrillary tangles of tau proteins. This accumulation triggers a complex cascade of cytotoxic, neuroinflammatory, and oxidative stresses that lead to neuronal death throughout the progression of the disease. Much of research in AD focused on the 2 pathologic proteins. Interestingly, another form of dementia with similar clinical manifestations of AD, but preferentially affected much older individuals, was termed as limbic-predominant age-related transactive response DNA-binding protein 43 (TDP-43) encephalopathy (LATE) and involved the cytotoxic intraneuronal deposition of phosphorylated TDP-43. TDP-43 proteinopathy was also found to be involved in AD pathology leading to the possibility that AD and LATE may share a common upstream etiology. This paper discusses the roles molecular pathways known in AD may have on influencing TDP-43 proteinopathy and the development of AD, LATE, or the 2 being comorbid with each other.

Utility of FDG-PET in diagnosis of Alzheimer-related TDP-43 proteinopathy.

OBJECTIVE: To evaluate FDG-PET as an antemortem diagnostic tool for Alzheimer-related TAR DNA-binding protein of 43 kDa (TDP-43) proteinopathy. METHODS: We conducted a cross-sectional neuroimaging-histologic analysis of patients with antemortem FDG-PET and postmortem brain tissue from the Mayo Clinic Alzheimer's Disease Research Center and Study of Aging with Alzheimer spectrum pathology. TDP-43-positive status was assigned when TDP-43-immunoreactive inclusions were identified in the amygdala. Statistical parametric mapping (SPM) analyses compared TDP-43-positive (TDP-43[+]) with TDP-43-negative cases (TDP-43[-]), correcting for field strength, sex, Braak neurofibrillary tangle, and neuritic plaque stages. Cross-validated logistic regression analyses were used to determine whether regional FDG-PET values predict TDP-43 status. We also assessed the ratio of inferior temporal to medial temporal (IMT) metabolism as this was proposed as a biomarker of hippocampal sclerosis. RESULTS: Of 73 cases, 27 (37%) were TDP-43(+), of which 6 (8%) had hippocampal sclerosis. SPM analysis showed TDP-43(+) cases having greater hypometabolism of medial temporal, frontal superior medial, and frontal supraorbital (FSO) regions (p unc < 0.001). Logistic regression analysis showed only FSO and IMT to be associated with TDP-43(+) status, identifying up to 81% of TDP-43(+) cases (p < 0.001). An IMT/FSO ratio was superior to the IMT in discriminating TDP-43(+) cases: 78% vs 48%, respectively. CONCLUSIONS: Alzheimer-related TDP-43 proteinopathy is associated with hypometabolism in the medial temporal and frontal regions. Combining FDG-PET measures from these regions may be useful for antemortem prediction of Alzheimer-related TDP-43 proteinopathy. CLASSIFICATION OF EVIDENCE: This study provides Class II evidence that hypometabolism in the medial temporal and frontal regions on FDG-PET is associated with Alzheimer-related TDP-43 proteinopathy.

High glycine content in TDP-43: a potential culprit in limbic-predominant age-related TDP-43 encephalopathy.

Numerous risk factors for heart disease or dementia harbor over 10% valine plus glycine content. Interestingly, TDP-43 contains 6.0% valine and 13.3% glycine, and the buildup of this protein in the brains of patients with limbic-predominant age-related TDP-43 encephalopathy has dire consequences. The two γ-methyl groups in valine enable hyperconjugation, which enhances the van der Waals interaction between its side group and the carbonyl carbon. This extends the C=O bond length, and this weakened C=O bond augments the secondary chemical bonding of the carbonyl oxygen atom to cations. This, in turn, promotes the formation and buildup of insoluble and rigid salts such as calcium oxalate, which is postulated to be a major cause of heart disease. Similarly, the long C=O bond length in glycine results in a weakened C=O bond with an enhanced affinity toward cations and the formation of insoluble salts. Further, several prion proteins possess a high glycine content of approximately 20%. The insoluble calcium salts produced may promote aggregate formation via secondary chemical bonding between calcium and glycine, as well as between calcium and valine. Chemical and biochemical insights will help us to better understand the etiology of disorders linked to protein aggregates.

Tau and TDP-43 proteinopathies: kindred pathologic cascades and genetic pleiotropy.

We review the literature on Tau and TDP-43 proteinopathies in aged human brains and the relevant underlying pathogenetic cascades. Complex interacting pathways are implicated in Alzheimer's disease and related dementias (ADRD), wherein multiple proteins tend to misfold in a manner that is "reactive," but, subsequently, each proteinopathy may contribute strongly to the clinical symptoms. Tau proteinopathy exists in brains of individuals across a broad spectrum of primary underlying conditions-e.g., developmental, traumatic, and inflammatory/infectious diseases. TDP-43 proteinopathy is also expressed in a wide range of clinical disorders.  Although TDP-43 proteinopathy was first described in the central nervous system of patients with amyotrophic lateral sclerosis (ALS) and in subtypes of frontotemporal dementia (FTD/FTLD), TDP-43 proteinopathy is also present in chronic traumatic encephalopathy, cognitively impaired persons in advanced age with hippocampal sclerosis, Huntington's disease, and other diseases. We list known Tau and TDP-43 proteinopathies.  There is also evidence of cellular co-localization between Tau and TDP-43 misfolded proteins, suggesting common pathways or protein interactions facilitating misfolding in one protein by the other. Multiple pleiotropic gene variants can alter risk for Tau or TDP-43 pathologies, and certain gene variants (e.g., APOE ε4, Huntingtin triplet repeats) are associated with increases of both Tau and TDP-43 proteinopathies. Studies of genetic risk factors have provided insights into multiple nodes of the pathologic cascades involved in Tau and TDP-43 proteinopathies. Variants from a specific gene can be either a low-penetrant risk factor for a group of diseases, or alternatively, a different variant of the same gene may be a disease-driving allele that is associated with a relatively aggressive and early-onset version of a clinically and pathologically specific disease type. Overall, a complex but enlightening paradigm has emerged, wherein both Tau and TDP-43 proteinopathies are linked to numerous overlapping upstream influences, and both are associated with multiple downstream pathologically- and clinically-defined deleterious effects.

TDP-43 causes neurotoxicity and cytoskeletal dysfunction in primary cortical neurons.

TDP-43-mediated proteinopathy is a key factor in the pathology of amyotrophic lateral sclerosis (ALS). A potential underlying mechanism is dysregulation of the cytoskeleton. Here we investigate the effects of expressing TDP-43 wild-type and M337V and Q331K mutant isoforms on cytoskeletal integrity and function, using rat cortical neurons in vitro. We find that TDP-43 protein becomes mislocalised in axons over 24-72 hours in culture, with protein aggregation occurring at later timepoints (144 hours). Quantitation of cell viability showed toxicity of both wild-type and mutant constructs which increased over time, especially of the Q331K mutant isoform. Analysis of the effects of TDP-43 on axonal integrity showed that TDP-43-transfected neurons had shorter axons than control cells, and that growth cone sizes were smaller. Axonal transport dynamics were also impaired by transfection with TDP-43 constructs. Taken together these data show that TDP-43 mislocalisation into axons precedes cell death in cortical neurons, and that cytoskeletal structure and function is impaired by expression of either TDP-43 wild-type or mutant constructs in vitro. These data suggest that dysregulation of cytoskeletal and neuronal integrity is an important mechanism for TDP-43-mediated proteinopathy.

Traumatic brain injury causes frontotemporal dementia and TDP-43 proteolysis.

Traumatic brain injury (TBI) is a major risk factor for dementia. Recently, TBI has also been suggested as a risk factor for frontotemporal dementia (FTD), and plasma immunoreactivity to the TAR-DNA binding protein 43 (TDP-43) has been observed in both patients with acute TBI and long-term survivors of this condition. We used a population-based study to estimate and compare the risk of FTD in individuals with and without TBI. Furthermore, we used a rat model of TBI to show that increased TDP-43 proteolysis following TBI produces FTD-like impairments, including abnormal limb-clasping, and impaired performances in the Morris water maze. We recruited 24,585 patients who received ambulatory or hospital care for TBI and 122,925 patients without TBI for this study. Each individual was investigated for 4years to evaluate FTD development, and data were analyzed by Cox proportional hazard regression. In the TBI rat model, behavior and TDP-43 inclusions were assessed following intracranial administration of a caspase-3 inhibitor or vehicle. FTD was more likely to occur in the TBI group than in the group without TBI (adjusted hazard ratio, 4.43; 95% confidence interval, 3.85-5.10; P<0.001). Rats developed behavioral impairments similar to those in patients with FTD after TBI. Further, the behavioral impairments were likely associated with TDP-43 short fragment mislocalization and accumulation. Our findings suggest that in humans, TBI is associated with a greater occurrence of FTD. Moreover, clinical FTD manifestations may be associated with TDP-43 proteolysis, since impaired behaviors in TBI rats were reminiscent of those in humans with FTD.

[New therapeutic approaches]. / Neue Therapieansätze.

The most prevalent causes of dementia are progressive and irreversible neurodegenerative diseases of the brain. Alzheimer's disease ranks first and is follwed by Parkinson and Lewy body disease as well as the Frontotemporal lobar degenerations. These neurodegenerative processes are characterised by the production, aggregation and deposition of pathological proteins. These are ß amyloid and tau in Alzheimer's disease; α synuclein in der Parkinson's- and Lewy body disease, and tau, TDP-43 as well as FUS in the Frontotemporal lobar degenerations. Aggregation into oligomers and fibrils and subsequent sedimentation of these proteins lead to nerve cell dysfunction, synaptic failure and ultimately to the demise of neurons. The deficits and imbalance of neurotransmitter systems which represent an important target of the current pharmacological treatment of dementia are consequences of nerve cell loss. Many of the novel treatment approaches that are being tested in clinical trials are aimed at preventing, slowing or ameliorating the production, aggregation and deposition of pathological proteins. Key strategies are inhibition of secretases which generate ß amyloid, active and passive immunisation against ß amyloid, restriction ß amyloid and tau aggregation as well as stimulation of ß amyloid clearance. In addition clinical trials are ongoing on symptomatic treatments including the simultaneous stimulation of multiple neurotransmitter systems, compensation of brain insulin resistance, and neuroprotection through certain nutrients. In addition to novel drug treatments non-pharmacological interventions are also being developed.

TDP-43 proteinopathy and motor neuron disease in chronic traumatic encephalopathy.

Epidemiological evidence suggests that the incidence of amyotrophic lateral sclerosis is increased in association with head injury. Repetitive head injury is also associated with the development of chronic traumatic encephalopathy (CTE), a tauopathy characterized by neurofibrillary tangles throughout the brain in the relative absence of ß-amyloid deposits. We examined 12 cases of CTE and, in 10, found a widespread TAR DNA-binding protein of approximately 43kd (TDP-43) proteinopathy affecting the frontal and temporal cortices, medial temporal lobe, basal ganglia, diencephalon, and brainstem. Three athletes with CTE also developed a progressive motor neuron disease with profound weakness, atrophy, spasticity, and fasciculations several years before death. In these 3 cases, there were abundant TDP-43-positive inclusions and neurites in the spinal cord in addition to tau neurofibrillary changes, motor neuron loss, and corticospinal tract degeneration. The TDP-43 proteinopathy associated with CTE is similar to that found in frontotemporal lobar degeneration with TDP-43 inclusions, in that widespread regions of the brain are affected. Akin to frontotemporal lobar degeneration with TDP-43 inclusions, in some individuals with CTE, the TDP-43 proteinopathy extends to involve the spinal cord and is associated with motor neuron disease. This is the first pathological evidence that repetitive head trauma experienced in collision sports might be associated with the development of a motor neuron disease.

[TDP-43 proteinopathies, toward understanding of the molecular pathogenesis].

The TDP-43 proteinopathies: Toward understanding of the molecular pathogenesis. TAR DNA binding protein of 43 kDa (TDP-43), a heterogeneous nuclear ribonucleoprotein was identified as a major component of ubiquitin-positive inclusions in FTLD and ALS, and the concept of TDP-43 proteinopathies was proposed. Immunoblot and immunohistochemical analyses using multiple anti-phosphorylated TDP-43 antibodies revealed that hyperphosphorylated 18-26 kDa C-terminal fragments in addition to the full-length TDP-43 are major constituents of inclusions in FTLD-U and ALS. Recent discovery of mutations in the TDP-43 gene in familial and sporadic ALS, indicating that abnormality of TDP-43 protein cause neurodegeneration. It also strongly suggests that aggregation of TDP-43 or the process is responsible for neurodegeneration in FTLD-U and ALS. To investigate the molecular mechanisms of aggregation of TDP-43, we have established two cellular models for intracellular aggregates of TDP-43 similar to those in brains of TDP-43 proteinopathies patients. The first consists of SH-SY5Y cells expressing mutant TDP-43 that lacks both the nuclear localization signal (NLS) and residues 187-192 (deltaNLS & 187-192). The second model consists of SH-SY5Y cells expressing an aggregation-prone TDP-43 C-terminal fragment as a green fluorescent protein (GFP)-fusion. In these cells, round structures positive for both anti-pS409/410 and anti-Ub are observed. These results suggest that intracellular localization of TDP-43, truncation of TDP-43 and proteasomal dysfunction of cells may be involved in the pathological process of TDP-43 proteinopathies. We also found that two small compounds that have been reported to be beneficial in phase II clinical trials of Alzheimer's disease, inhibited the formation of TDP-43 aggregates in these two cellular models, suggesting that these compounds may be effective for the treatment of ALS and FTLD-U.