Abstract
A growing body of evidence suggests that a loss of chromosome 9 open reading frame 72 (C9ORF72) expression, formation of dipeptide-repeat proteins, and generation of RNA foci contribute to disease pathogenesis in amyotrophic lateral sclerosis and frontotemporal dementia. Although the levels of C9ORF72 transcripts and dipeptide-repeat proteins have already been examined thoroughly, much remains unknown about the role of RNA foci in C9ORF72-linked diseases. As such, we performed a comprehensive RNA foci study in an extensive pathological cohort of C9ORF72 expansion carriers (n = 63). We evaluated two brain regions using a newly developed computer-automated pipeline allowing recognition of cell nuclei and RNA foci (sense and antisense) supplemented by manual counting. In the frontal cortex, the percentage of cells with sense or antisense RNA foci was 26 or 12%, respectively. In the cerebellum, 23% of granule cells contained sense RNA foci and 1% antisense RNA foci. Interestingly, the highest percentage of cells with RNA foci was observed in cerebellar Purkinje cells (~70%). In general, more cells contained sense RNA foci than antisense RNA foci; however, when antisense RNA foci were present, they were usually more abundant. We also observed that an increase in the percentage of cells with antisense RNA foci was associated with a delayed age at onset in the frontal cortex (r = 0.43, p = 0.003), whereas no other associations with clinico-pathological features were seen. Importantly, our large-scale study is the first to provide conclusive evidence that RNA foci are not the determining factor of the clinico-pathological variability observed in C9ORF72 expansion carriers and it emphasizes that the distribution of RNA foci does not follow the pattern of neurodegeneration, stressing the complex interplay between different aspects of C9ORF72-related diseases.
Highlights
Three mechanisms by which a repeat expansion in chromosome 9 open reading frame 72 (C9ORF72) might be causative of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) [11, 31] are a loss of C9ORF72Acta Neuropathol (2017) 134:255–269 expression [11], the formation of dipeptide-repeat proteins aberrantly translated from the repeat [2, 27], and the generation of RNA foci containing flawed RNA transcripts [11]
We examined RNA foci in patients carrying a repeat expansion in C9ORF72 (n = 63), using computer-automated pipelines combined with manual counting
RNA fluorescent in situ hybridization (FISH) coupled with immunofluorescence staining revealed neuronal cells as well as glial cells; RNA foci were often seen in neuronal cells, but were rare in glial cells, aligning with previous studies [19, 26]
Summary
Acta Neuropathol (2017) 134:255–269 expression [11], the formation of dipeptide-repeat proteins aberrantly translated from the repeat [2, 27], and the generation of RNA foci containing flawed RNA transcripts [11]. While studies focusing on the levels of C9ORF72 transcripts and dipeptide-repeat proteins did not fully explain the clinical and pathological variability observed in C9ORF72 expansion carriers [15, 39], we seek to elucidate the role that RNA foci play in C9ORF72-linked diseases. The first report revealing RNA foci in patients carrying C9ORF72 repeat expansions demonstrated that they are present in approximately 25% of cells in the frontal cortex and spinal cord, and it has been hypothesized that they may sequester RNA-binding proteins, potentially disrupting mRNA splicing [11]. It has been shown that RNA foci can contain both sense and antisense transcripts [14, 43], which suggests that bidirectional transcription occurs
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
