The 5’-Untranslated Region of the C9orf72 mRNA Exhibits a Phylogenetic Alignment to the Cis-Aconitase Iron-Responsive Element; Novel Therapies for Amytrophic Lateral Sclerosis

Abstract

The hexanucleotide repeat mutation in the intron-1 of the chromosome 9 open reading frame (C9orf72) is a frequent cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Altered RNA folding plays a role in ALS pathogenesis in two ways: non-ATG translation of the repeat can lead to aggregates of the known C9orf72 specific dipeptide polymer, whereas the repeat also can form neurotoxic RNA inclusions that dose-responsively kill motor neurons. We report the presence of a homology in the 5'untranslated region (UTR) of the messenger RNA encoding C9orf72 with the iron responsive elements (IRE) that control expression of iron-associated transcripts and predict that this RNA structure may iron-dependently regulate C9orf72 translation. We previously report altered serum ferritin levels track with severity of ALS in patients. Here, we conduct bioinformatics analyses to determine the secondary structure of the 5'UTR in C9orf72 mRNA and find it aligned with IREs in the human mitochondrial cis-aconitase and L and H-ferritin transcripts. Comparison of the role of RNA repeats in Friedriech's ataxia and fragile X mental retardation suggests the utility of RNA based therapies for treatment of ALS. Antisense oligonucleotides (ASO) have been reported to therapeutically target these GGGGCC repeats. At the same time, because the function of C9orf72 is unknown, knockdown strategies carry some risk of inducing or compounding haploinsufficiency. We propose, for consideration, an approach that may enhance its therapeutic dynamic range by increasing the 5'UTR driven translation of C9orf72 protein to compensate for any potential ALS-specific or ASO-induced haploinsufficieny.

Targeting the Iron-Response Elements of the mRNAs for the Alzheimer’s Amyloid Precursor Protein and Ferritin to Treat Acute Lead and Manganese Neurotoxicity

“…The APP 5’UTR is a uniquely folded RNA structure that is related, though distinct from, the functional IRE in the transcript of the iron storage protein ferritin, though it is base paired in a unique RNA architecture [9,11,17,27]. While there is evidence for a spectrum of IRE like homologies in neurodegenerative disease transcripts [28], the translational control model in Figure 1 summarizes the means by which the APP 5’UTR, while acting in response to iron [11,17], was also sufficiently uniquely folded to act as an anti-amyloid target for the FDA pre-approved anti-cholinesterase phenserine and its enantiomer posiphen [1]. Phenserine and its enantiomer posiphen are each in the class of APP 5’UTR directed drugs that were first identified using transfection-based studies to inhibit APP in cell culture [20] and also limit amyloid Aβ levels in vivo [1].…”