Genetic report abstractSerum microRNAs in sporadic amyotrophic lateral sclerosis
Introduction
Amyotrophic lateral sclerosis (ALS) is characterized by a progressive loss of motor neurons and fatal outcome within 3–5 years (Rowland and Shneider, 2001). About 10% of ALS cases are familial (fALS) and approximately half to two-thirds thereof can be explained by mutations in known ALS genes. The remaining 90% are sporadic cases (sALS) with infrequent mutations in known ALS genes (Renton et al., 2014).
Growing evidence implicates messenger RNA (mRNA) but most recently also microRNA (miRNA) dysmetabolism in ALS disease pathogenesis (Goodall et al., 2013). Twenty to 24 nucleotides mature miRNAs are mostly inhibitory post-transcriptional regulators of gene expression (Chekulaeva and Filipowicz, 2009). miRNAs are involved in the cellular response to various stressors and insults (Liu et al., 2013, Mendell and Olson, 2012, Viader et al., 2011, Zhang et al., 2013). Thereby, miRNA expression profiles can reflect activation of specific pathogenic pathways. Dysregulation of miRNA expression has been reported, for example, in the SOD1-G93A mouse model of ALS or patient-derived tissue (Butovsky et al., 2012, Campos-Melo et al., 2013, De Felice et al., 2012, Toivonen et al., 2014).
miRNAs are remarkably stable in serum and other body fluids as exosomal cargos or bound to specific proteins (Xu et al., 2012), and disease-related changes of extracellular miRNA abundance has been repeatedly shown. Although the causative involvement of these changes in disease pathogenesis is still unclear, they are at least thought to represent reactive events related to specific pathways of neurodegeneration. In the context of ALS, alterations in the peripheral miRNA abundance have been suggested to represent a systemic dysfunction of ubiquitously expressed, RNA binding proteins that are involved in ALS pathogenesis (Burgos et al., 2014, Freischmidt et al., 2013, Freischmidt et al., 2014, Gandhi et al., 2013).
In a recent study, we identified 30 miRNAs significantly downregulated in the serum of fALS patients that were largely independent from the underlying disease gene. Most of these miRNAs (22) were already downregulated in presymptomatic ALS mutation carriers, even years before the estimated disease onset. Moreover, downregulated miRNAs shared a common nucleotide consensus motif possibly indicating specific protein binding partners and downstream pathways common for different ALS genes (Freischmidt et al., 2014).
In this study, we examined serum miRNA profiles of sporadic ALS patients and compared them to miRNA signatures of fALS patients (Freischmidt et al., 2014). We show that, serum miRNA profiles are far more heterogeneous in sALS than in fALS. At the same time, however, a considerable proportion of sALS patients share miRNA signatures typical for fALS patients suggesting alteration of common pathways and a high contribution of genetic factors also to sporadic ALS.
Section snippets
Patient cohorts and ethics statement
Blood samples were drawn in accordance with the Declaration of Helsinki (World Medical Association, 1964), and study protocols were approved by the national medical ethical review boards. Participants provided prior written informed consent.
ALS patients fulfilling the El-Escorial criteria for definite ALS were considered sporadic cases due to a known negative family history of the disease. Additionally, the 2 main genetic causes of familial ALS, namely mutations in the SOD1 gene and a
Serum miRNA profiles of sALS patients are highly heterogeneous
In the discovery experiment, relative serum miRNA levels of 18 sALS patients and 16 matched healthy controls (Supplementary Table 1) were compared using Affymetrix GeneChip miRNA 3.0 Arrays. To exclude any false positive changes of miRNA abundance, we restricted our analysis to downregulated miRNAs that are not susceptible to increased hemolysis reported previously for ALS patients (Freischmidt et al., 2014, Ronnevi and Conradi, 1984).
We observed a significant downregulation of only 2 miRNAs (
Discussion
Here, we present a comprehensive array-based serum miRNA analysis of sALS patients revealing a highly heterogeneous serum miRNA profile pattern. This finding contrasts with the homogeneous serum miRNA signatures observed by the identical technique and the same ALS center in familial ALS cases as well as presymptomatic mutation carriers recently (Freischmidt et al., 2014). Nevertheless, we could identify 2 mature miRNAs consistently downregulated in serum of sALS patients. We, furthermore,
Disclosure statement
The authors have no actual or potential conflicts of interest.
Acknowledgements
The authors are indebted to the patients and their families for their participation in this project. The authors are grateful to their study nurse Antje Knehr and their technicians Nadine Todt and Elena Jasovskaja as well as the Ulm Neurology biobank team for excellent patient care and technical assistance. The authors thank Dr. Michael Bonin and Dr. Michael Walter (University of Tübingen) for access to and help with IPA. This work was supported in whole or in parts by grants from the German
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