Paul M. McKeever

Isoform-specific antibodies reveal distinct subcellular localizations of C9orf72 in amyotrophic lateral sclerosis.

A noncoding hexanucleotide repeat expansion in C9orf72 is the most common cause of amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD). It has been reported that the repeat expansion causes a downregulation of C9orf72 transcripts, suggesting that haploinsufficiency may contribute to disease pathogenesis. Two protein isoforms are generated from three alternatively spliced transcripts of C9orf72; a long form (C9‐L) and a short form (C9‐S), and their function(s) are largely unknown owing to lack of specific antibodies.

Unaffected mosaicC9orf72case: RNA foci, dipeptide proteins, but upregulated C9orf72 expression

Objective Suggested C9orf72 disease mechanisms for amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration include C9orf72 haploinsufficiency, G4C2/C4G2 RNA foci, and dipeptide repeat (DPR) proteins translated from the G4C2 expansion; however, the role of small expansions (e.g., 30–90 repeats) is unknown and was investigated here. Methods We conducted a molecular and pathology study of a family in which the father (unaffected at age 90) carried a 70-repeat allele in blood DNA that expanded to ≈1,750 repeats in his children, causing ALS. Results Southern blotting revealed different degrees of mosaicism of small and large expansions in the fathers tissues from the CNS. Surprisingly, in each mosaic tissue, C9orf72 mRNA levels were significantly increased compared to an ALS-affected daughter with a large expansion. Increased expression correlated with higher levels of the 70-repeat allele (the upregulation was also evident at the protein level). Remarkably, RNA foci and DPR burdens were similar or even significantly increased (in cerebellum) in the unaffected father compared to the daughter with ALS. However, the father did not display TDP-43 pathology and signs of neurodegeneration. Conclusion The presence of RNA foci and DPR pathology was insufficient for disease manifestation and TDP-43 pathology in the mosaic C9orf72 carrier with upregulated C9orf72 expression. It is important to conduct an investigation of similar cases, which could be found among unaffected parents of sporadic C9orf72 patients (e.g., 21% among Finnish patients with ALS). Caution should be taken when consulting carriers of small expansions because disease manifestation could be dependent on the extent of the somatic instability in disease-relevant tissues.

Cholinergic neuron gene expression differences captured by translational profiling in a mouse model of Alzheimer's disease.

Cholinergic neurotransmission is impaired in Alzheimers disease (AD), and loss of basal forebrain cholinergic neurons is a key component of disease pathogenicity and symptomatology. To explore the molecular basis of this cholinergic dysfunction, we paired translating ribosome affinity purification (TRAP) with RNA sequencing (TRAP-Seq) to identify the actively translating mRNAs in anterior forebrain cholinergic neurons in the TgCRND8 mouse model of AD. Bioinformatic analyses revealed the downregulation of 67 of 71 known cholinergic-related transcripts, consistent with cholinergic neuron dysfunction in TgCRND8 mice, as well as transcripts related to oxidative phosphorylation, neurotrophins, and ribosomal processing. Upregulated transcripts included those related to axon guidance, glutamatergic synapses and kinase activity and included AD-risk genes Sorl1 and Ptk2b. In contrast, the total transcriptome of the anterior forebrain showed upregulation in cytokine signaling, microglia, and immune system pathways, including Trem2, Tyrobp, and Inpp5d. Hence, TRAP-Seq clearly distinguished the differential gene expression alterations occurring in cholinergic neurons of TgCRND8 mice compared with wild-type littermates, providing novel candidate pathways to explore for therapeutic development in AD.

Downregulation of exosomal miR-204-5p and miR-632 as a biomarker for FTD: a GENFI study

Objective To determine whether exosomal microRNAs (miRNAs) in cerebrospinal fluid (CSF) of patients with frontotemporal dementia (FTD) can serve as diagnostic biomarkers, we assessed miRNA expression in the Genetic Frontotemporal Dementia Initiative (GENFI) cohort and in sporadic FTD. Methods GENFI participants were either carriers of a pathogenic mutation in progranulin, chromosome 9 open reading frame 72 or microtubule-associated protein tau or were at risk of carrying a mutation because a first-degree relative was a known symptomatic mutation carrier. Exosomes were isolated from CSF of 23 presymptomatic and 15 symptomatic mutation carriers and 11 healthy non-mutation carriers. Expression of 752 miRNAs was measured using quantitative PCR (qPCR) arrays and validated by qPCR using individual primers. MiRNAs found differentially expressed in symptomatic compared with presymptomatic mutation carriers were further evaluated in a cohort of 17 patients with sporadic FTD, 13 patients with sporadic Alzheimer’s disease (AD) and 10 healthy controls (HCs) of similar age. Results In the GENFI cohort, miR-204-5p and miR-632 were significantly decreased in symptomatic compared with presymptomatic mutation carriers. Decrease of miR-204-5p and miR-632 revealed receiver operator characteristics with an area of 0.89 (90% CI 0.79 to 0.98) and 0.81 (90% CI 0.68 to 0.93), respectively, and when combined an area of 0.93 (90% CI 0.87 to 0.99). In sporadic FTD, only miR-632 was significantly decreased compared with AD and HCs. Decrease of miR-632 revealed an area of 0.90 (90% CI 0.81 to 0.98). Conclusions Exosomal miR-204-5p and miR-632 have potential as diagnostic biomarkers for genetic FTD and miR-632 also for sporadic FTD.

PROFILING EXOSOMAL MIRNAS IN EARLY ONSET ALZHEIMER’S DISEASE CEREBROSPINAL FLUID

and the covariance parameters between the baseline CSF Ab42, TAU and PTAU volume change over time indicated that OSA participants experienced a faster decrease in CSF Ab42 and increases in TAU and PTAU volumes over time (p < .0001 for all) in both the CN and MCI groups. Conclusions: OSA possibly accelerates longitudinal changes in brain amyloid deposition, and CSF biomarkers burden, both in elderly cognitive normal and MCI individuals. Further research examining mechanisms underlying these observed effects are needed.

Elucidating the gene expression changes that underpin cholinergic dysfunction in a mouse model of Alzheimer’s disease

were selected among those exhibiting the strongest variation in terms of fluorescence intensity (the 2.5 % highest and lowest variations). From the selected, enrichment pathway analysis were performed using the Ingenuity database. Results:Data for 18,049 different genes were generated after our different control processes and we finally selected 820 hits showing strong impact on the APP metabolism. Pathway enrichment analysis identified canonical-pathways such as IGF-1 signaling (P1⁄41.1E-05), Cholesterol Biosynthesis (P1⁄41.5E-05) and JAK/ Stat Signaling (P1⁄42.2E05). Among the 150 genes localized in the known susceptibility loci, 7 genes were identified as modulator of APP metabolism. Conclusions: Characterization of these modulators could be useful for our in-depth understanding of the APP metabolism and to characterize the impact of the GWAS-defined genetic risk factors on the AD physiopathology.