TDP-43 is a component of ubiquitin-positive tau-negative inclusions in frontotemporal lobar degeneration and amyotrophic lateral sclerosis

Recently, TDP-43 was identified as a key component of ubiquitinated aggregates in amyotrophic lateral sclerosis (ALS), an adult-onset neurological disorder that leads to the degeneration of motor neurons. Here we report eight missense mutations in nine individuals--six from individuals with sporadic ALS (SALS) and three from those with familial ALS (FALS)--and a concurring increase of a smaller TDP-43 product. These findings further corroborate that TDP-43 is involved in ALS pathogenesis.

TARDBP mutations in individuals with sporadic and familial amyotrophic lateral sclerosis

The increased application of transcriptome-wide profiling approaches has led to an explosion in the number of documented long non-coding RNAs (lncRNAs). While these new and enigmatic players in the complex transcriptional milieu are encoded by a significant proportion of the genome, their functions are mostly unknown. Early discoveries support a paradigm in which lncRNAs regulate transcription via chromatin modulation, but new functions are steadily emerging. Given the biochemical versatility of RNA, lncRNAs may be used for various tasks, including post-transcriptional regulation, organization of protein complexes, cell-cell signalling and allosteric regulation of proteins.

/pdf/rna-in-unexpected-places-long-non-coding-rna-functions-in-2cdl2nfa83.pdf

RNA in unexpected places: long non-coding RNA functions in diverse cellular contexts

We used cross-linking and immunoprecipitation coupled with high-throughput sequencing to identify binding sites in 6,304 genes as the brain RNA targets for TDP-43, an RNA binding protein that, when mutated, causes amyotrophic lateral sclerosis. Massively parallel sequencing and splicing-sensitive junction arrays revealed that levels of 601 mRNAs were changed (including Fus (Tls), progranulin and other transcripts encoding neurodegenerative disease-associated proteins) and 965 altered splicing events were detected (including in sortilin, the receptor for progranulin) following depletion of TDP-43 from mouse adult brain with antisense oligonucleotides. RNAs whose levels were most depleted by reduction in TDP-43 were derived from genes with very long introns and that encode proteins involved in synaptic activity. Lastly, we found that TDP-43 autoregulates its synthesis, in part by directly binding and enhancing splicing of an intron in the 3' untranslated region of its own transcript, thereby triggering nonsense-mediated RNA degradation.

/pdf/long-pre-mrna-depletion-and-rna-missplicing-contribute-to-4ijz4ygdlo.pdf

Long pre-mRNA depletion and RNA missplicing contribute to neuronal vulnerability from loss of TDP-43

TDP-43 is a predominantly nuclear RNA-binding protein that forms inclusion bodies in frontotemporal lobar degeneration (FTLD) and amyotrophic lateral sclerosis (ALS). The mRNA targets of TDP-43 in the human brain and its role in RNA processing are largely unknown. Using individual nucleotide-resolution ultraviolet cross-linking and immunoprecipitation (iCLIP), we found that TDP-43 preferentially bound long clusters of UG-rich sequences in vivo. Analysis of RNA binding by TDP-43 in brains from subjects with FTLD revealed that the greatest increases in binding were to the MALAT1 and NEAT1 noncoding RNAs. We also found that binding of TDP-43 to pre-mRNAs influenced alternative splicing in a similar position-dependent manner to Nova proteins. In addition, we identified unusually long clusters of TDP-43 binding at deep intronic positions downstream of silenced exons. A substantial proportion of alternative mRNA isoforms regulated by TDP-43 encode proteins that regulate neuronal development or have been implicated in neurological diseases, highlighting the importance of TDP-43 for the regulation of splicing in the brain.

/pdf/characterizing-the-rna-targets-and-position-dependent-5fdpwhv2ge.pdf

Characterizing the RNA targets and position-dependent splicing regulation by TDP-43

TDP43 is a human low molecular weight neurofilament (hNFL) mRNA-binding protein

Lack of TDP-43 abnormalities in mutant SOD1 transgenic mice shows disparity with ALS.

Traditionally, amyotrophic lateral sclerosis (ALS) has been considered to be a disorder in which the primary pathology resides in the degeneration of motor neurons, giving rise to progressive, diffuse muscle wasting, weakness, and spasticity. This view is rapidly being challenged to include a more widespread disease process in which motor system degeneration remains the core feature but not the sole system affected. Although its incidence remains to be determined, the evidence of cognitive impairment in ALS is overwhelming. However, it is important to recognize that there is likely to exist a continuum of cognitive dysfunction in ALS, ranging from mild cognitive impairment (ALSci) to a more fulminant progressive dementia of the frontotemporal type (FTD) with a small subset with an aphasic pattern. Most commonly, ALSci is reported as a subtle neurological presentation marked by deficits primarily in frontal and temporal functions. Although in the Japanese population, alterations in cognition have been reported to precede the motor system manifestations, typically the cognitive dysfunction follows the onset of neuromuscular deficits. Individuals with bulbar-onset disease appear to be at greater risk for the development of cognitive impairment, although these deficits are found to a lesser degree in limb-onset patients. Typical impairments include alterations in mental flexibility, verbal and nonverbal fluency, abstract reasoning, and memory, for both verbal and visual material. Less often, there is a rapidly progressive aphasic dementia. ALSci language characteristics include word-finding difficulty, lexical disorganization, and reliance on stereotypical sentences. Anterior-based language functions (eg, fluency, syntax, and grammar) are compromised. The relationship between FTD, FTD with ALS, and FTD with the neuropathological features of ALS in the absence of clinical findings remains to be clarified. There is likely to be significant overlap among these entities, as illustrated in a study of 36 FTD patients with no known diagnosis of ALS, 5 of whom met clinical and electrophysiological criteria for a definite diagnosis of ALS and an additional 13 who met criteria for possible ALS, of whom 1 subsequently developed ALS. The converse is also true. A study of word generation tests in 100 consecutive ALS patients identified a subset of 44 patients with impairments. Of these, diminished word generation was found in one third. Of this latter group, nearly all were shown to meet research criteria for FTD. In addition, one quarter of the patients with normal word generation who agreed to further evaluation met research criteria for FTD; these patients had new-onset personality changes. In addition to the precentral gyrus atrophy that is well recognized in ALS, neuroimaging in ALSci demonstrates a more widespread frontal and temporal cortical atrophy, with variable involvement of the precentral and postcentral gyrus, the anterior cingulate gyrus, corpus callosum, and brainstem tegmentum. Functional neuroimaging techniques, including single-positron emission tomography studies with either I-Nisopropyl-p-iodoamphetamine or Tc-d,l-hexamethylproplene–amine oxime (HM-PAO), and positron emission tomography, are sensitive to reduced frontal and temporal cortical blood flow in ALSci. Reductions in the N-acetylaspartase to creatine ratio of anterior cingulate gyrus neurons with the use of proton magnetic resonance spectroscopy has been shown to be a sensitive marker of ALSci. The typical neuropathological features of ALS include degeneration of the descending supraspinal motor pathways and their neurons of origin, and of brainstem and spinal motor neurons in addition to

Cognitive impairment, frontotemporal dementia, and the motor neuron diseases

Background: The authors compared tau protein deposition in the frontal cortex of patients with cognitive impairment of amyotrophic lateral sclerosis (ALSci) (n = 6), cognitively intact patients with ALS (n = 6), and age-matched controls (n = 6) in order to determine the pathologic substrate of ALSci Methods: Archival paraffin-embedded tissue was examined using Gallyas staining and immunostaining for tau-1 (phosphorylation-dependent tau epitope), tau-2 (phosphorylation independent), Alzheimer-specific tau phosphoepitopes (AT 8; ser396 phosphorylation), β-amyloid, glial fibrillary acid protein, SMI 31 (recognizing phosphorylated NFH), α-synuclein, or ubiquitin Results: Tau immunoreactive astrocytic and dense neuronal inclusions were found in both ALS and ALSci, although to a greater extent in ALSci Superficial linear spongiosis and Gallyas-positive intraneuronal aggregates, immunoreactive with tau-1 and AT 8 but rarely to ser396 tau, were unique to ALSci Dense extracellular aggregates were observed by both Gallyas staining and tau-1 immunostaining Tufted degenerating astrocytes containing tau-1 and AT 8 immunoreactive aggregates and, rarely, dense Gallyas positive neuritic plaques immunoreactive with tau-1 and AT 8, but not with ser396 tau or β-amyloid, were observed in ALSci Tau positive glial coiled bodies were observed in the deep cortical layers and adjacent subcortical white matter in ALSci Although 3R and 4R tau mRNA isoforms were expressed to similar levels in the frontal cortex of all cases, the total amount of tau mRNA was increased in both ALS and ALSci Both gray and white matter soluble tau protein expression was similar among control, ALS, and ALSci cases Conclusions: Cognitive dysfunction in ALS may reflect abnormal tau protein metabolism

Wencheng Yang

Papers

TDP43 is a human low molecular weight neurofilament (hNFL) mRNA-binding protein

Lack of TDP-43 abnormalities in mutant SOD1 transgenic mice shows disparity with ALS.

Cognitive impairment, frontotemporal dementia, and the motor neuron diseases

Microtubule-associated tau protein positive neuronal and glial inclusions in ALS.

Upregulation of GSK3β expression in frontal and temporal cortex in ALS with cognitive impairment (ALSci)