MTHFSD and DDX58 are novel RNA-binding proteins abnormally regulated in amyotrophic lateral sclerosis

Abstract

Tar DNA-binding protein 43 (TDP-43) is an RNA-binding protein normally localized to the nucleus of cells, where it elicits functions related to RNA metabolism such as transcriptional regulation and alternative splicing. In amyotrophic lateral sclerosis, TDP-43 is mislocalized from the nucleus to the cytoplasm of diseased motor neurons, forming ubiquitinated inclusions. Although mutations in the gene encoding TDP-43, TARDBP, are found in amyotrophic lateral sclerosis, these are rare. However, TDP-43 pathology is common to over 95% of amyotrophic lateral sclerosis cases, suggesting that abnormalities of TDP-43 play an active role in disease pathogenesis. It is our hypothesis that a loss of TDP-43 from the nucleus of affected motor neurons in amyotrophic lateral sclerosis will lead to changes in RNA processing and expression. Identifying these changes could uncover molecular pathways that underpin motor neuron degeneration. Here we have used translating ribosome affinity purification coupled with microarray analysis to identify the mRNAs being actively translated in motor neurons of mutant TDP-43(A315T) mice compared to age-matched non-transgenic littermates. No significant changes were found at 5 months (presymptomatic) of age, but at 10 months (symptomatic) the translational profile revealed significant changes in genes involved in RNA metabolic process, immune response and cell cycle regulation. Of 28 differentially expressed genes, seven had a ≥ 2-fold change; four were validated by immunofluorescence labelling of motor neurons in TDP-43(A315T) mice, and two of these were confirmed by immunohistochemistry in amyotrophic lateral sclerosis cases. Both of these identified genes, DDX58 and MTHFSD, are RNA-binding proteins, and we show that TDP-43 binds to their respective mRNAs and we identify MTHFSD as a novel component of stress granules. This discovery-based approach has for the first time revealed translational changes in motor neurons of a TDP-43 mouse model, identifying DDX58 and MTHFSD as two TDP-43 targets that are misregulated in amyotrophic lateral sclerosis.

Physiological functions and pathobiology of TDP‐43 and FUS/TLS proteins

“…The list of potential translation targets important for neurodegeneration, however, is likely to increase. For instance, the use of a translational profile approach to identify mRNAs actively translated in motor neurons of a TDP-43 animal model allowed two additional mRNAs (MTHFSD and DDX58) that are directly bound by TDP-43 and whose translation may be altered in the spinal cord of these mice to be identified (MacNair et al 2015).…”

Copy number variations of MTHFSD gene across pig breeds and its association with litter size traits in Chinese indigenous Xiang pig

“…Recently, MacNair et al. () have reported MTHFSD is a novel RNA‐binding protein, which contain an RNA recognition motif (RRM). Therefore, we speculate MTHFSD as RNA‐binding protein may play a significant role in MTHFS mRNA metabolism.…”

Altered mRNP granule dynamics in FTLD pathogenesis

“…Finally, a similar polysome profiling approach (translating ribosome affinity purification, TRAP) in motor neurons of a TDP‐43 mouse model identified two additional TDP‐43 mRNA targets ( MTHFSD and DDX58 ) that may be translationally regulated by TDP‐43 (MacNair et al . ). It should be noted that another study that used polysome profile analysis in HeLa cells did not find TDP‐43 in polysome fractions (Higashi et al .…”