The long non-coding RNA nuclear-enriched abundant transcript 1-2 induces paraspeckle formation in the motor neuron during the early phase of amyotrophic lateral sclerosis

Background: A long non-coding RNA (lncRNA), nuclear-enriched abundant transcript 1-2 (NEAT1-2), constitutes nuclear bodies known as "paraspeckles". Mutations of RNA binding proteins, including TAR DNA-binding protein-43 (TDP-43) and fused in sarcoma/translocated in liposarcoma (FUS/TLS), have been described in amyotrophic lateral sclerosis (ALS). ALS is a devastating motor neuron disease, which progresses rapidly to a total loss of upper and lower motor neurons, with consciousness sustained. The aim of this study was to clarify the interaction of paraspeckles with ALS-associated RNA-binding proteins, and to identify increased occurrence of paraspeckles in the nucleus of ALS spinal motor neurons. Results: In situ hybridization (ISH) and ultraviolet cross-linking and immunoprecipitation were carried out to investigate interactions of NEAT1-2 lncRNA with ALS-associated RNA-binding proteins, and to test if paraspeckles form in ALS spinal motor neurons. As the results, TDP-43 and FUS/TLS were enriched in paraspeckles and bound to NEAT1-2 lncRNA directly. The paraspeckles were localized apart from the Cajal bodies, which were also known to be related to RNA metabolism. Analyses of 633 human spinal motor neurons in six ALS cases showed NEAT1-2 lncRNA was upregulated during the early stage of ALS pathogenesis. In addition, localization of NEAT1-2 lncRNA was identified in detail by electron microscopic analysis combined with ISH for NEAT1-2 lncRNA. The observation indicating specific assembly of NEAT1-2 lncRNA around the interchromatin granule-associated zone in the nucleus of ALS spinal motor neurons verified characteristic paraspeckle formation. Conclusions: NEAT1-2 lncRNA may act as a scaffold of RNAs and RNA binding proteins in the nuclei of ALS motor neurons, thereby modulating the functions of ALS-associated RNA-binding proteins during the early phase of ALS. These findings provide the first evidence of a direct association between paraspeckle formation and a neurodegenerative disease, and may shed light on the development of novel therapeutic targets for the treatment of ALS.