Activity-regulated RNA editing in select neuronal subfields in hippocampus

RNA editing by adensosine deaminases is a widespread mechanism to alter genetic information in metazoa. In addition to modifications in non-coding regions, editing contributes to diversification of protein function, in analogy to alternative splicing. However, although splicing programs respond to external signals, facilitating fine tuning and homeostasis of cellular functions, a similar regulation has not been described for RNA editing. Here, we show that the AMPA receptor R/G editing site is dynamically regulated in the hippocampus in response to activity. These changes are bi-directional, reversible and correlate with levels of the editase Adar2. This regulation is observed in the CA1 hippocampal subfield but not in CA3 and is thus subfield/celltype-specific. Moreover, alternative splicing of the flip/flop cassette downstream of the R/G site is closely linked to the editing state, which is regulated by Ca(2+). Our data show that A-to-I RNA editing has the capacity to tune protein function in response to external stimuli

<i>C9ORF72</i> repeat expansion causes vulnerability of motor neurons to Ca²⁺-permeable AMPA receptor-mediated excitotoxicity

Funded by The Wellcome Trust (Grant 092742/Z/10/Z), MNDA (Miles/Oct14/878-792), MRC, Euan MacDonald Centre, UK DRI, DBT-India, ISSF (WT/UoE), Royal Society of Edinburgh (CRF), and Biogen/UoE Joint Discovery Research Collaboration. RNA-Seq raw reads were generated by Edinburgh Genomics, The University of Edinburgh. Edinburgh Genomics is partly supported through core grants from NERC (R8/H10/56), MRC (MR/K001744/1), and BBSRC (BB/J004243/1).Mutations in C9ORF72 are the most common cause of familial amyotrophic lateral sclerosis (ALS). Here, through a combination of RNA-seq and electrophysiological studies on induced pluripotent stem cell (iPSC) derived motor neuron (MNs), we show that increased expression of GluA1 AMPA receptor (AMPAR) subunit occurs in MNs with C9ORF72 mutations that leads to increased Ca2+-permeable AMPAR expression and results in enhanced selective MN vulnerability to excitotoxicity. These deficits are not found in iPSC-derived cortical neurons and are abolished by CRISPR/Cas9-mediated correction of the C9ORF72 repeat expansion in MNs. We also demonstrate that MN-specific dysregulation of AMPAR expression is also present in C9ORF72 patient post mortem material. We therefore present multiple lines of evidence for the specific upregulation of GluA1 subunits in human mutant C9ORF72 MNs that could lead to a potential pathogenic excitotoxic mechanism in ALS.Publisher PDFPeer reviewe

A positron emission tomography study on the role of nigral lesions in parkinsonism in patients with amyotrophic lateral sclerosis

Background Patients with amyotrophic lateral sclerosis (ALS) sometimes exhibit parkinsonism, but the lesion responsible for parkinsonism has not been extensively studied. Objective To test whether nigrostriatal system dysfunction is responsible for parkinsonism in ALS. Design From the 182 ALS patients who were admitted to our neurology ward during the past 10 years, we extracted all the patients who satisfied the criteria of both parkinsonism and ALS. Setting The University of Tokyo Hospital. Methods We conducted [18F]L-dopa and [11C]N-methylspiperone positron emission tomography and technetium Tc 99m hexamethylpropyleneamine oxime single-photon emission computed tomography studies on 5 patients with ALS manifesting overt parkinsonism. Results Two male and 3 female patients (average age, 63.2 \ub1 5.8 years) had ALS for an average of 28.6 \ub1 21.5 months and had parkinsonism for an average of 15.2 \ub1 11.4 months. Features of their parkinsonism were characterized by outstanding bradykinesia without resting tremor or dementia. The results of positron emission tomography studies indicated normal nigrostriatal function, but those of single-photon emission computed tomography demonstrated decreased blood flow in the frontotemporal cortices. Conclusion It is likely that parkinsonism in ALS is due to cortical lesions rather than nigrostriatal dysfunction and that both symptoms are the clinical manifestation of frontotemporal dementia with motor neuron diseases, including classic ALS

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Co-Occurrence of TDP-43 Mislocalization with Reduced Activity of an RNA Editing Enzyme, ADAR2, in Aged Mouse Motor Neurons

<div><p>TDP-43 pathology in spinal motor neurons is a neuropathological hallmark of sporadic amyotrophic lateral sclerosis (ALS) and has recently been shown to be closely associated with the downregulation of an RNA editing enzyme called adenosine deaminase acting on RNA 2 (ADAR2) in the motor neurons of sporadic ALS patients. Because TDP-43 pathology is found more frequently in the brains of elderly patients, we investigated the age-related changes in the TDP-43 localization and ADAR2 activity in mouse motor neurons. We found that ADAR2 was developmentally upregulated, and its mRNA expression level was progressively decreased in the spinal cords of aged mice. Motor neurons normally exhibit nuclear ADAR2 and TDP-43 immunoreactivity, whereas fast fatigable motor neurons in aged mice demonstrated a loss of ADAR2 and abnormal TDP-43 localization. Importantly, these motor neurons expressed significant amounts of the Q/R site-unedited AMPA receptor subunit 2 (GluA2) mRNA. Because expression of unedited GluA2 has been demonstrated as a lethality-causing molecular abnormality observed in the motor neurons, these results suggest that age-related decreases in ADAR2 activity play a mechanistic role in aging and serve as one of risk factors for ALS.</p> </div