Co-aggregation of RNA binding proteins in ALS spinal motor neurons: Evidence of a common pathogenic mechanism

Department of Pathology, Western University, 1151 Richmond Street, London, ON, N6A 5K8, Canada.
Acta Neuropathologica (Impact Factor: 10.76). 09/2012; 124(5):733-47. DOI: 10.1007/s00401-012-1035-z
Source: PubMed


While the pathogenesis of amyotrophic lateral sclerosis (ALS) remains to be clearly delineated, there is mounting evidence that altered RNA metabolism is a commonality amongst several of the known genetic variants of the disease. In this study, we evaluated the expression of 10 ALS-associated proteins in spinal motor neurons (MNs) in ALS patients with mutations in C9orf72 (C9orf72(GGGGCC)-ALS; n = 5), SOD1 (mtSOD1-ALS; n = 9), FUS/TLS (mtFUS/TLS-ALS; n = 2), or TARDBP (mtTDP-43-ALS; n = 2) and contrasted these to cases of sporadic ALS (sALS; n = 4) and familial ALS without known mutations (fALS; n = 2). We performed colorimetric immunohistochemistry (IHC) using antibodies against TDP-43, FUS/TLS, SOD1, C9orf72, ubiquitin, sequestosome 1 (p62), optineurin, phosphorylated high molecular weight neurofilament, peripherin, and Rho-guanine nucleotide exchange factor (RGNEF). We observed that RGNEF-immunoreactive neuronal cytoplasmic inclusions (NCIs) can co-localize with TDP-43, FUS/TLS and p62 within spinal MNs. We confirmed their capacity to interact by co-immunoprecipitations. We also found that mtSOD1-ALS cases possess a unique IHC signature, including the presence of C9orf72-immunoreactive diffuse NCIs, which allows them to be distinguished from other variants of ALS at the level of light microscopy. These findings support the hypothesis that alterations in RNA metabolism are a core pathogenic pathway in ALS. We also conclude that routine IHC-based analysis of spinal MNs may aid in the identification of families not previously suspected to harbor SOD1 mutations.

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Available from: Cristian Droppelmann, Apr 17, 2014
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    • "Representative image of RGNEF cytoplasmic inclusions observed in motor neurons of ALS patients (indicated by arrows) compared with a control case. Immunohistochemistry was performed as described previously (Keller et al., 2012; Droppelmann et al., 2013a) using goat polyclonal anti-RGNEF (MediMabs; 1:500 dilution; Scale bar = 10 μm). "
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    ABSTRACT: Small GTPases participate in a broad range of cellular processes such as proliferation, differentiation, and migration. The exchange of GDP for GTP resulting in the activation of these GTPases is catalyzed by a group of enzymes called guanine nucleotide exchange factors (GEFs), of which two classes: Dbl-related exchange factors and the more recently described dedicator of cytokinesis proteins family exchange factors. Increasingly, deregulation of normal GEF activity or function has been associated with a broad range of disease states, including neurodegeneration and neurodevelopmental disorders. In this review, we examine this evidence with special emphasis on the novel role of Rho guanine nucleotide exchange factor (RGNEF/p190RhoGEF) in the pathogenesis of amyotrophic lateral sclerosis. RGNEF is the first neurodegeneration-linked GEF that regulates not only RhoA GTPase activation but also functions as an RNA binding protein that directly acts with low molecular weight neurofilament mRNA 3' untranslated region to regulate its stability. This dual role for RGNEF, coupled with the increasing understanding of the key role for GEFs in modulating the GTPase function in cell survival suggests a prominent role for GEFs in mediating a critical balance between cytotoxicity and neuroprotection which, when disturbed, contributes to neuronal loss.
    Frontiers in Cellular Neuroscience 09/2014; 8. DOI:10.3389/fncel.2014.00282 · 4.29 Impact Factor
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    • "Although genetic variation in OPTN is rare in ALS patients in other populations, pathologic studies confirm a role for OPTN in ALS. In SALS cases, OPTN is present in cytoplasmic skein-like inclusions and colocalizes with ubiquitin, TDP-43, and possibly FUS [46, 85, 103, 135, 159] (Table 1). Conflicting results are obtained with respect to OPTN immunoreactivity in SOD1 and FUS mutation carriers. "
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    ABSTRACT: Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by the aggregation of ubiquitinated proteins in affected motor neurons. Recent studies have identified several new molecular constituents of ALS-linked cellular aggregates, including FUS, TDP-43, OPTN, UBQLN2 and the translational product of intronic repeats in the gene C9ORF72. Mutations in the genes encoding these proteins are found in a subgroup of ALS patients and segregate with disease in familial cases, indicating a causal relationship with disease pathogenesis. Furthermore, these proteins are often detected in aggregates of non-mutation carriers and those observed in other neurodegenerative disorders, supporting a widespread role in neuronal degeneration. The molecular characteristics and distribution of different types of protein aggregates in ALS can be linked to specific genetic alterations and shows a remarkable overlap hinting at a convergence of underlying cellular processes and pathological effects. Thus far, self-aggregating properties of prion-like domains, altered RNA granule formation and dysfunction of the protein quality control system have been suggested to contribute to protein aggregation in ALS. The precise pathological effects of protein aggregation remain largely unknown, but experimental evidence hints at both gain- and loss-of-function mechanisms. Here, we discuss recent advances in our understanding of the molecular make-up, formation, and mechanism-of-action of protein aggregates in ALS. Further insight into protein aggregation will not only deepen our understanding of ALS pathogenesis but also may provide novel avenues for therapeutic intervention. Electronic supplementary material The online version of this article (doi:10.1007/s00401-013-1125-6) contains supplementary material, which is available to authorized users.
    Acta Neuropathologica 05/2013; 125(6). DOI:10.1007/s00401-013-1125-6 · 10.76 Impact Factor
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