Severe subcortical TDP-43 pathology in sporadic frontotemporal lobar degeneration with motor neuron disease

Tar DNA binding protein-43 (TDP-43) associates with stress granules: analysis of cultured cells and pathological brain tissue

Tar DNA Binding Protein-43 (TDP-43) is a principle component of inclusions in many cases of frontotemporal lobar degeneration (FTLD-U) and amyotrophic lateral sclerosis (ALS). TDP-43 resides predominantly in the nucleus, but in affected areas of ALS and FTLD-U central nervous system, TDP-43 is aberrantly processed and forms cytoplasmic inclusions. The mechanisms governing TDP-43 inclusion formation are poorly understood. Increasing evidence indicates that TDP-43 regulates mRNA metabolism by interacting with mRNA binding proteins that are known to associate with RNA granules. Here we show that TDP-43 can be induced to form inclusions in cell culture and that most TDP-43 inclusions co-localize with SGs. SGs are cytoplasmic RNA granules that consist of mixed protein-RNA complexes. Under stressful conditions SGs are generated by the reversible aggregation of prion-like proteins, such as TIA-1, to regulate mRNA metabolism and protein translation. We also show that disease-linked mutations in TDP-43 increased TDP-43 inclusion formation in response to stressful stimuli. Biochemical studies demonstrated that the increased TDP-43 inclusion formation is associated with accumulation of TDP-43 detergent insoluble complexes. TDP-43 associates with SG by interacting with SG proteins, such as TIA-1, via direct protein-protein interactions, as well as RNA-dependent interactions. The signaling pathway that regulates SGs formation also modulates TDP-43 inclusion formation. We observed that inclusion formation mediated by WT or mutant TDP-43 can be suppressed by treatment with translational inhibitors that suppress or reverse SG formation. Finally, using Sudan black to quench endogenous autofluorescence, we also demonstrate that TDP-43 positive-inclusions in pathological CNS tissue co-localize with multiple protein markers of stress granules, including TIA-1 and eIF3. These data provide support for accumulating evidence that TDP-43 participates in the SG pathway.

Amyotrophic lateral sclerosis: dash-like accumulation of phosphorylated TDP-43 in somatodendritic and axonal compartments of somatomotor neurons of the lower brainstem and spinal cord

Skein-like and spherical inclusions within the somatodendritic compartment of a few types of susceptible neurons in the human nervous system are the currently acknowledged pathological hallmarks of amyotrophic lateral sclerosis (ALS). These inclusions consist chiefly of an aggregated, phosphorylated, and ultimately ubiquitinated intranuclear protein, TDP-43. To investigate the development of these inclusions, a single neuronal type that is susceptible to the ALS-associated pathological process, i.e., the class of large multipolar somatomotor neurons in the lower brainstem and spinal cord, was studied in four cases of sporadic ALS and four age-matched controls using immunoreactions against phosphorylated TDP-43 (pTDP-43), p62, and ubiquitin. In these neurons, the protein TDP-43, after its displacement outside of the cell nucleus and abnormal phosphorylation, forms light microscopically visible dash-like aggregates which were dispersed throughout their entire somatodendritic domain and even extended into the proximal portions of the axon. Many motor neurons contained these lesions, which were not detectable with anti-TDP-43 and anti-p62. In an additional step, a small number of the neurons that contain the dash-like lesions displayed a clustering of the aggregated material, which forms thick net-like (potential precursors of the skein-like inclusions) and spherical inclusions. This material, in turn, was ubiquitinated and p62-immunopositive. Thus, dash-like pTDP-43 aggregates are regularly seen in motor neurons in ALS and may represent the initial cellular lesion in this disease. Because these aggregates were not stained with antibodies against p62 and non-phosphorylated TDP-43, it is possible that phosphorylation of TDP-43 is required for its aggregation in sporadic ALS.

TDP-43 and FUS/TLS: emerging roles in RNA processing and neurodegeneration

Amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD) are neurodegenerative diseases with clinical and pathological overlap. Landmark discoveries of mutations in the transactive response DNA-binding protein (TDP-43) and fused in sarcoma/translocated in liposarcoma (FUS/TLS) as causative of ALS and FTLD, combined with the abnormal aggregation of these proteins, have initiated a shifting paradigm for the underlying pathogenesis of multiple neurodegenerative diseases. TDP-43 and FUS/TLS are both RNA/DNA-binding proteins with striking structural and functional similarities. Their association with ALS and other neurodegenerative diseases is redirecting research efforts toward understanding the role of RNA processing regulation in neurodegeneration.

Transgenic rat model of neurodegeneration caused by mutation in the TDP gene

TDP-43 proteinopathies have been observed in a wide range of neurodegenerative diseases. Mutations in the gene encoding TDP-43 (i.e., TDP) have been identified in amyotrophic lateral sclerosis (ALS) and in frontotemporal lobe degeneration associated with motor neuron disease. To study the consequences of TDP mutation in an intact system, we created transgenic rats expressing normal human TDP or a mutant form of human TDP with a M337V substitution. Overexpression of mutant, but not normal, TDP caused widespread neurodegeneration that predominantly affected the motor system. TDP mutation reproduced ALS phenotypes in transgenic rats, as seen by progressive degeneration of motor neurons and denervation atrophy of skeletal muscles. This robust rat model also recapitulated features of TDP-43 proteinopathies including the formation of TDP-43 inclusions, cytoplasmic localization of phosphorylated TDP-43, and fragmentation of TDP-43 protein. TDP transgenic rats will be useful for deciphering the mechanisms underlying TDP-43–related neurodegenerative diseases.

Amyotrophic lateral sclerosis, a condition also known as Lou Gehrig's disease, is characterized by progressive degeneration of motor neurons, denervation atrophy of skeletal muscles, and eventual paralysis of affected limbs. The signature pathology of Lou Gehrig's disease is the formation of intracellular inclusions containing phosphorylated TDP-43 protein. Most cases of Lou Gehrig's disease do not have a clear cause, while only about 10% of the cases are caused by mutation of individual genes. Here, we describe a novel rat model that expresses a mutated form of the human gene encoding TDP-43 and manifests the phenotypes and pathological features observed in patients with Lou Gehrig's disease. Laboratory rats are the preferred animals for pharmacological studies. Therefore, this new rat model will be useful not only for mechanistic study of Lou Gehrig's disease, but also for the development of therapies for this devastating disease.

TAR DNA-binding protein 43 in neurodegenerative disease

In 2006, TAR DNA-binding protein 43 (TDP-43), a highly conserved nuclear protein, was identified as the major disease protein in amyotrophic lateral sclerosis (ALS) and in the most common variant of frontotemporal lobar degeneration (FTLD), FTLD-U, which is characterized by cytoplasmic inclusions that stain positive for ubiquitin but negative for tau and alpha-synuclein. Since then, rapid advances have been made in our understanding of the physiological function of TDP-43 and the role of this protein in neurodegeneration. These advances link ALS and FTLD-U (now designated FTLD-TDP) to a shared mechanism of disease. In this Review, we summarize the current evidence regarding the normal function of TDP-43 and the TDP-43 pathology observed in FTLD-TDP, ALS, and other neurodegenerative diseases wherein TDP-43 pathology co-occurs with other disease-specific lesions (for example, with amyloid plaques and neurofibrillary tangles in Alzheimer disease). Moreover, we discuss the accumulating data that support our view that FTLD-TDP and ALS represent two ends of a spectrum of primary TDP-43 proteinopathies. Finally, we comment on the importance of recent advances in TDP-43-related research to neurological practice, including the new opportunities to develop better diagnostics and disease-modifying therapies for ALS, FTLD-TDP, and related disorders exhibiting TDP-43 pathology.

Progressive anterior operculum syndrome due to FTLD-TDP: a clinico-pathological investigation

Pathological investigation of progressive anterior operculum syndrome has rarely been reported. We describe clinico-pathological findings in a patient with progressive anterior operculum syndrome. A 74-year-old right-handed man had noticed speech and swallowing difficulties 1 year previously. Neurological examinations showed no abnormality other than a slight limitation of upward gaze and slow tongue movement without fibrillation. We investigated the patient using neuroimaging and neuropsychological examinations and observed him for 2 years until his death, at which point we obtained pathological findings. The patient's facial and masseteric muscles seemed hypotonic with drooling, but he could laugh and yawn normally, showing automatic voluntary dissociation. Palatal and pharyngeal reflexes were normal. Magnetic resonance imaging showed cortical atrophy in the temporal lobes bilaterally. (123)IMP single photon emission computed tomography and positron emission tomography showed decreased blood flow and activity in the frontotemporal lobes, predominantly on the left side. Neuropsychological examinations showed no aphasia, dementia or other neuropsychological abnormality. Intubation fiberscopy, laryngoscopy and video fluorography showed no abnormality. After 6 months his anarthria and dysphagia became aggravated. He died of aspiration pneumonia 2 years after onset. Postmortem examination revealed neuronal degeneration with TDP-43-positive inclusions in the frontal, temporal and insular cortices, consistent with frontotemporal lobar degeneration with TDP inclusions (FTLD-TDP). However, neuronal loss with gliosis was more prominent in the inferior part of the motor cortices, bilaterally. Progressive anterior operculum syndrome could be classified as a variant of FTLD-TDP.

Amyotrophic lateral sclerosis and frontotemporal lobar degeneration: a spectrum of TDP-43 proteinopathies

It is now established that pathological transactive response DNA-binding protein with a Mr of 43 kD (TDP-43) on sodium dodecyl sulfate-polyacrylamide gel electrophoresis is the major disease protein in amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD) with ubiquitin-positive inclusions (now known as FTLD-TDP). In fact, the discovery of pathological TDP-43 solidified the idea that these disorders are multi-system diseases and this led to the concept of a TDP-43 proteinopathy as a spectrum of disorders comprised of different clinical and pathological entities extending from ALS to ALS with cognitive impairment/dementia and FTLD-TDP without or with motor neuron disease (FTLD-MND). These align along a broad disease continuum sharing similar pathogenetic mechanisms linked to pathological TDP-43. We here review salient findings in the development of a concept of TDP-43 proteinopathy as a novel group of neurodegenerative diseases similar in concept to alpha-synucleinopathies and tauopathies.

Transactivation response DNA-binding protein 43 microvasculopathy in frontotemporal degeneration and familial Lewy body disease

We describe novel transactivation response DNA-binding protein of 43 kd (TDP-43)-positive structures in the brains of patients with frontotemporal lobar degeneration with ubiquitin-positive inclusions and familial Lewy body disease. The TDP-43 immunohistochemistry revealed small round structures closely associated with small blood vessels. By immunoelectron microscopy, these TDP-43-positive structures were unmyelinated cell processes located adjacent to and sometimes enclosed by the capillary basal lamina. Some processes protruded from outside of the vascular basal lamina to a position beneath the basal lamina. The processes contained 10- to 17-nm-diameter straight filaments or filaments coated with granular material similar to those described in neurites in frontotemporal lobar degeneration with ubiquitin-positive inclusions and other disorders. In some of the abnormal structures, electron-dense material formed paracrystalline arrays composed of TDP-43. The inclusions were variably positive by immunostaining for the small heat shock protein alphaB-crystallin and less often glial fibrillary acidic protein. Bundles of astrocytic glial fibrils characteristic of reactive astrocytes were often found in proximity, but glial fibrils were negative for TDP-43. These data suggest that these processes are astrocytic end-feet with abnormal TDP-43 fibrillary inclusions. The significance of this novel TDP-43 microvasculopathy on blood-brain barrier integrity warrants further investigation.

Knockdown of transactive response DNA-binding protein (TDP-43) downregulates histone deacetylase 6

TDP-43 is an RNA/DNA-binding protein implicated in transcriptional repression and mRNA processing. Inclusions of TDP-43 are hallmarks of frontotemporal dementia and amyotrophic lateral sclerosis. Besides aggregation of TDP-43, loss of nuclear localization is observed in disease. To identify relevant targets of TDP-43, we performed expression profiling. Thereby, histone deacetylase 6 (HDAC6) downregulation was discovered on TDP-43 silencing and confirmed at the mRNA and protein level in human embryonic kidney HEK293E and neuronal SH-SY5Y cells. This was accompanied by accumulation of the major HDAC6 substrate, acetyl-tubulin. HDAC6 levels were restored by re-expression of TDP-43, dependent on RNA binding and the C-terminal protein interaction domains. Moreover, TDP-43 bound specifically to HDAC6 mRNA arguing for a direct functional interaction. Importantly, in vivo validation in TDP-43 knockout Drosophila melanogaster confirmed the specific downregulation of HDAC6. HDAC6 is necessary for protein aggregate formation and degradation. Indeed, HDAC6-dependent reduction of cellular aggregate formation and increased cytotoxicity of polyQ-expanded ataxin-3 were found in TDP-43 silenced cells. In conclusion, loss of functional TDP-43 causes HDAC6 downregulation and might thereby contribute to pathogenesis.

Concentrations of beta-amyloid precursor protein processing products in cerebrospinal fluid of patients with amyotrophic lateral sclerosis and frontotemporal lobar degeneration

Frontotemporal lobar degeneration (FTLD) and amyotrophic lateral sclerosis (ALS) are neurodegenerative disorders with heterogeneous clinical presentation but common neuropathological characteristics and pathophysiological substrates, which led to the view of ALS and FTLD representing two manifestations of a clinicopathological spectrum. For both diseases, changes in metabolism of beta-amyloid precursor protein (APP) are reported. In a pilot study, we analyzed cerebrospinal fluid from patients of the ALS-FTLD spectrum for APP processing products. ALS patients show elevated absolute levels of soluble APP and a shift towards the nonamyloidogenic APP processing pathway in contrast to patients with FTLD or ALS + FTLD. Changes in Abeta pattern could be described, allowing separation of patients with pure FTLD from ALS + FTLD. Combination of sAPP and Abeta values improves group differentiation. These findings may provide information on pathophysiological processes in the ALS-FTLD disease spectrum and could have impact in neurochemical diagnosis. We propose to expand this study to larger patient groups comprising followed up cases with known neuropathology.

The molecular basis of frontotemporal dementia

Frontotemporal dementia (FTD) is a clinical syndrome with a heterogeneous molecular basis. Familial FTD has been linked to mutations in several genes, including those encoding the microtubule-associated protein tau (MAPT), progranulin (GRN), valosin-containing protein (VCP) and charged multivescicular body protein 2B (CHMP2B). The associated neuropathology is characterised by selective degeneration of the frontal and temporal lobes (frontotemporal lobar degeneration, FTLD), usually with the presence of abnormal intracellular protein accumulations. The current classification of FTLD neuropathology is based on the identity of the predominant protein abnormality, in the belief that this most closely reflects the underlying pathogenic process. Major subgroups include those characterised by the pathological tau, TDP-43, intermediate filaments and a group with cellular inclusions composed of an unidentified ubiquitinated protein. This review will focus on the current understanding of the molecular basis of each of the major FTLD subtypes. It is anticipated that this knowledge will provide the basis of future advances in the diagnosis and treatment of FTD.

Clinical and pathological continuum of multisystem TDP-43 proteinopathies

OBJECTIVE

To determine the extent of transactivation response DNA-binding protein with a molecular weight of 43 kDa (TDP-43) pathology in the central nervous system of patients with clinically and autopsy-confirmed diagnoses of frontotemporal lobar degeneration with and without motor neuron disease and amyotrophic lateral sclerosis with and without cognitive impairment.

DESIGN

Performance of immunohistochemical whole-central nervous system scans for evidence of pathological TDP-43 and retrospective clinical medical record review.

SETTING

An academic medical center.

PARTICIPANTS

We included 64 patients with clinically and pathologically confirmed frontotemporal lobar degeneration with ubiquitinated inclusions with or without motor neuron disease and amyotrophic lateral sclerosis with or without cognitive impairment.

MAIN OUTCOME MEASURE

Neuronal and glial TDP-43 pathology.

RESULTS

We found evidence of neuronal and glial TDP-43 pathology in all disease groups throughout the neuraxis, albeit with variations in the frequency, morphology, and distribution of TDP-43 lesions. Moreover, the major clinical manifestations (eg, cognitive impairments, motor neuron signs, extrapyramidal symptoms, neuropsychiatric features) were reflected by the predominant distribution and burden of TDP-43 pathology.

CONCLUSION

These findings strongly suggest that amyotrophic lateral sclerosis, frontotemporal lobar degeneration with amyotrophic lateral sclerosis or motor neuron disease, and frontotemporal lobar degeneration with ubiquitinated inclusions are different manifestations of a multiple-system TDP-43 proteinopathy linked to similar mechanisms of neurodegeneration.

TDP-43 redistribution is an early event in sporadic amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder consisting of progressive loss of motor neurons. TDP-43 has been identified as a component of ubiquitin-immunoreactive inclusions of motor neurons in ALS. We focused on the diffuse cytoplasmic TDP-43 immunoreactivity in ALS neurons, and quantitatively assessed it in comparison with skein/round TDP-43 and ubiquitin immunostaining in motor neurons of 30 sporadic ALS cases. The percentage of spinal motor neurons with cytoplasmic TDP-43 immunoreactivity was higher than that of ubiquitin-immunoreactive ones. The percentage of TDP-43-positive motor neurons was independent of neuron counts in anterior horns, while the percentage of ubiquitinated neurons was inversely correlated. Aiming to define the cytosolic localization of TDP-43, the immunoblot analysis of spinal cord and frontal cortex showed that full-length TDP-43, the 45 kDa form and ubiquitinated TDP-43 are found in the soluble inclusion-free fraction. The present data suggest that delocalization, accumulation and ubiquitination of TDP-43 in the cytoplasm of motor neurons are early dysfunctions in the cascade of the events leading to motor neuron degeneration in ALS, preceding the formation of insoluble inclusion bodies. Being cytoplasmic accumulation an ongoing event during the course of the illness, a therapeutic approach to this incurable disease can be envisaged.

Amyotrophic lateral sclerosis, frontotemporal dementia and beyond: the TDP-43 diseases

Ever since the significance of pathological 43-kDa transactivating responsive sequence DNA-binding protein (TDP-43) for human disease has been recognized in amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration with ubiquitin positive inclusions (FTLD-U), a number of publications have emerged reporting on this pathology in a variety of neurodegenerative diseases. Given the heterogeneous and, in part, conflicting nature of the recent findings, we here review pathological TDP-43 and its relationship to human disease with a special focus on ALS and FTLD-U. To this end, we propose a classification scheme in which pathological TDP-43 is the major disease defining pathology in one group, or is present in addition to other neurodegenerative hallmark pathologies in a second category. We conclude that the TDP-43 proteinopathies represent a novel class of neurodegenerative disorders akin to alpha-synucleinopathies and tauopathies, with the concept of ALS and FTLD-U to be widened to a broad clinico-pathological multisystem disease, i.e., TDP-43 proteinopathy.

Molecular neuropathology of TDP-43 proteinopathies

The identification of TDP-43 as the major component of the pathologic inclusions in most forms of sporadic and familial frontotemporal lobar degeneration with ubiquitin-positive inclusions (FTLD-U) and amyotrophic lateral sclerosis (ALS) resolved a long-standing enigma concerning the nature of the ubiquitinated disease protein under these conditions. Anti-TDP-43 immunohistochemistry and the recent development of novel tools, such as phosphorylation-specific TDP-43 antibodies, have increased our knowledge about the spectrum of pathological changes associated with FTLD-U and ALS and moreover, facilitated the neuropathological routine diagnosis of these conditions. This review summarizes the recent advances in our understanding on the molecular neuropathology and pathobiology of TDP-43 in FTLD and ALS.

Sporadic amyotrophic lateral sclerosis of long duration is associated with relatively mild TDP-43 pathology

Recently, sporadic amyotrophic lateral sclerosis (SALS), a fatal neurological disease, has been shown to be a multisystem proteinopathy of TDP-43 in which both neurons and glial cells in the central nervous system are widely affected. In general, the natural history of SALS is short (<5 years). However, it is also known that a few patients may survive for 10 years or more, even without artificial respiratory support (ARS). In the present study using TDP-43 immunohistochemistry, we examined various regions of the nervous system in six patients with SALS of long duration (10-20 years) without ARS, in whom lower motor-predominant disease with Bunina bodies and ubiquitinated inclusions (UIs) in the affected lower motor neurons was confirmed. One case also showed UIs in the hippocampal dentate granule cells (UDG). In all cases, except one with UDG, the occurrence of TDP-43-immunoreactive (ir) neuronal cytoplasmic inclusions (NCIs) was confined to a few regions in the spinal cord and brainstem, including the anterior horns. In one case with UDG, TDP-43-ir NCIs were also detected in the substantia nigra, and some regions of the cerebrum, including the hippocampal dentate gyrus (granule cells). The number of neurons displaying NCIs in each region was very small (1-3 per region, except the dentate gyrus). On the other hand, the occurrence of TDP-43-ir glial cytoplasmic inclusions (GCIs) was more widespread in the central nervous system, including the cerebral white matter. Again, however, the number of glial cells displaying GCIs in each region was very small (1-3 per region). In conclusion, compared to the usual form of SALS, TDP-43 pathology shown in SALS of long duration was apparently mild in degree and limited in distribution, corresponding to the relatively benign clinical courses observed. It is now apparent that SALS of long duration is actually part of a TDP-43 proteinopathy spectrum.

TDP-43 in cerebrospinal fluid of patients with frontotemporal lobar degeneration and amyotrophic lateral sclerosis

BACKGROUND

Recently, TAR DNA-binding protein 43 (TDP-43) was identified as the major component of ubiquitin-positive tau-negative neuronal and glial inclusions in the most common form of frontotemporal lobar degeneration (FTLD) and in amyotrophic lateral sclerosis (ALS). It was demonstrated that different TDP-43 profiles correspond to clinical phenotypes of FTLD or ALS subgroups, and the differential diagnostic potential of TDP-43 was suggested.

OBJECTIVES

To examine TDP-43 in cerebrospinal fluid (CSF) and to analyze whether it could serve as a diagnostic marker.

DESIGN

We characterized CSF TDP-43 by immunoblot using different TDP-43 antibodies and determined the relative TDP-43 levels in CSF samples from patients.

SETTING

Academic research.

PATIENTS

Twelve patients with FTLD, 15 patients with ALS, 9 patients with ALS plus FTLD, 3 patients with ALS plus additional signs of frontal disinhibition, and 13 control subjects.

MAIN OUTCOME MEASURES

Results of TDP-43 immunoblot.

RESULTS

Polyclonal TDP-43 antibodies recognized a 45-kDa band in all analyzed samples. Two monoclonal and N-terminus-specific antibodies did not detect any specific bands, but C-terminus-specific antibodies detected a 45-kDa band and additional bands at approximately 20 kDa in all CSF samples. Relative quantification of 45-kDa bands revealed significant differences among the diagnostic groups (P =.046). Specifically, patients with ALS (P =.03) and FTLD (P =.02) had higher TDP-43 levels than controls but with a prominent overlap of values.

CONCLUSION

Although there is no evidence of pathologically altered TDP-43 proteins in CSF, TDP-43 levels in CSF might aid in characterizing subgroups of patients across the ALS and FTLD disease spectrum.

Fine structural analysis of the neuronal inclusions of frontotemporal lobar degeneration with TDP-43 proteinopathy

TAR DNA-binding protein of 43 kDa (TDP-43) is a major component of the pathological inclusions of frontotemporal lobar degeneration with TDP-43 proteinopathy, also called FTLD with ubiquitin-positive, tau-negative inclusions (FTLD-U), and motor neuron disease (MND). TDP-43 is predominantly expressed in the nucleus and regulates gene expression and splicing. In FTLD with TDP-43 proteinopathy, neuronal inclusions present variably as cytoplasmic inclusions (NCIs), dystrophic neurites (DNs), and intranuclear inclusions (NIIs), leading to a fourfold neuropathological classification correlating with genotype. There have been few fine structural studies of these inclusions. Thus, we undertook an immunoelectron microscopic study of FTLD with TDP-43 proteinopathy, including sporadic and familial cases with progranulin (GRN) mutation. TDP-43-immunoreactive inclusions comprised two components: granular and filamentous. Filament widths, expressed as mean (range) were: NCI, 9 nm (4-16 nm); DN, 10 nm (5-16 nm); NII, 18 nm (9-50 nm). Morphologically distinct inclusion components may reflect the process of TDP-43 aggregation and interaction with other proteins: determining these latter may contribute towards understanding the heterogeneous pathogenesis of FTLD with TDP-43 proteinopathy.

Update on recent molecular and genetic advances in frontotemporal lobar degeneration

Great strides have been made in the last 2 years in the field of frontotemporal lobar degeneration (FTLD), particularly with respect to the genetics and molecular biology of FTLD with ubiquitinated inclusions. It is now clear that most cases of familial FTLD with ubiquitinated inclusions have mutations in the progranulin gene, located on chromosome 17. It is also clear that most ubiquitinated inclusions in FTLD with ubiquitinated inclusions are composed primarily of TAR DNA-binding protein-43. Thus, FTLDs can be separated into 2 major groups (i.e. tauopathies and ubiquitinopathies), and most of the ubiquitinopathies can now be defined as TAR DNA-binding protein-43 proteinopathies. Many of the familial FTLDs are linked to chromosome 17, including both the familial tauopathies and the familial TAR DNA-binding protein-43 proteinopathies with progranulin mutations. This review highlights the neuropathologic features and the most important discoveries of the last 2 years and places these findings into the historical context of FTLD.

Maturation process of TDP-43-positive neuronal cytoplasmic inclusions in amyotrophic lateral sclerosis with and without dementia

To elucidate the maturation process of TDP-43-positive neuronal inclusions, we immunohistochemically and immunoelectron-microscopically examined multiple areas from the brain and spinal cord from ten patients with amyotrophic lateral sclerosis (ALS) and 25 control subjects. TDP-43 immunohistochemistry demonstrated three types of inclusions in ALS: skein-like, round, and dot-like inclusions. Skein-like inclusions were found in all cases of ALS. Dot-like inclusions were found in the anterior horn in seven cases of ALS, all of whom had round inclusions, but not in cases without round inclusions. In addition, careful examination revealed two types of diffuse punctate cytoplasmic staining: linear wisps and punctate granules. Linear wisps were present in all cases of ALS but in none of 25 controls. In contrast, punctate granules were detected in all cases of ALS as well as in five of 13 normal and in seven of 12 diseased controls. Immunoelectron-microscopy revealed that skein-like inclusions consisted of granule-associated parallel filaments. Round and dot-like inclusions were composed of granulo-filamentous structures. However, punctate granules corresponded to the mitochondria and were not immunostained with anti-ubiquitin, indicating that punctate granules represent cross-reaction. We assumed that linear wisps ("fine skein") aggregate as thicker and longer threads ("coarse skein"), whereas round inclusions arise from dot-like inclusions. These findings suggest that there are differences in the formation process between skein-like and round inclusions, despite the antigenic and ultrastructural similarities.

Sporadic amyotrophic lateral sclerosis: two pathological patterns shown by analysis of distribution of TDP-43-immunoreactive neuronal and glial cytoplasmic inclusions

A nuclear protein, 43-kDa TAR DNA-binding protein (TDP-43), was recently identified as a component of the ubiquitinated inclusions (UIs) in frontotemporal lobar degeneration (FTLD-U) and sporadic amyotrophic lateral sclerosis (SALS). In the present study using immunohistochemistry, we examined various regions of the nervous system in a series of 35 SALS cases using a polyclonal antibody against TDP-43. Seven of the 35 cases had disease durations of more than 10 years with artificial respiratory support (ARS; duration: 69-156 months). In all cases, TDP-43-immunoreactive (ir) neuronal and glial cytoplasmic inclusions (NCIs and GCIs) were found together in many regions, including the histologically affected lower motor neuron nuclei. Cluster analysis of the distribution pattern of TDP-43-ir NCIs for cases without ARS (n = 28) identified two types (type 1, n = 16; type 2, n = 12). Type 2 was distinguished from type 1 by the presence of TDP-43-ir NCIs in the frontotemporal cortex, hippocampal formation, neostriatum and substantia nigra, and was significantly associated with dementia. Eleven of the 28 cases showed UIs in the hippocampal dentate granule cells, all of which had type-2 distribution pattern. Cases with ARS (n = 7) were also classified into the same types (type 1, n = 5; type 2, n = 2). Cases having type-1 distribution pattern (n = 21) showed no evident neuronal loss in most of the non-motor neuron nuclei where TDP-43-ir NCIs were present, whereas cases having type-2 distribution pattern (n = 14) often showed evident neuronal loss in the frontotemporal cortices, amygdaloid nuclei and substantia nigra. These findings indicate that SALS is a multisystem degenerative disease widely affecting both neurons and glial cells with a heterogeneous pattern of TDP-43-ir NCI distribution (SALS showing type-2 distribution pattern being closely linked to FTLD-U), and that long-term survival supported by a respirator has no apparent influence on the TDP-43 neuronal distribution pattern.