Super-Resolution Microscopy Reveals Presynaptic Localization of the ALS/FTD Related Protein FUS in Hippocampal Neurons.

Michael Schoen,Albert C Ludolph,Christian Proepper,Stefan Liebau,Stefan Putz,Jens Michaelis,Dhruva Deshpande,Michael J Schmeisser,Jochen M Reichel,Maria Demestre,Tobias M Boeckers

doi:10.3389/fncel.2015.00496

Michael Schoen, Albert C Ludolph + Show 9 more

Open Access

https://doi.org/10.3389/fncel.2015.00496

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Abstract

Fused in Sarcoma (FUS) is a multifunctional RNA-/DNA-binding protein, which is involved in the pathogenesis of the neurodegenerative disorders amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). A common hallmark of these disorders is the abnormal accumulation of mutated FUS protein in the cytoplasm. Under normal conditions FUS is confined to the nuclear compartment, in neurons, however, additional somatodendritic localization can be observed. In this study, we carefully analyzed the subcellular localization of endogenous FUS at synaptic sites of hippocampal neurons which are among the most affected cell types in FTD with FUS pathology. We could confirm a strong nuclear localization of FUS as well as its prominent and widespread neuronal expression throughout the adult and developing rat brain, particularly in the hippocampus, the cerebellum and the outer layers of the cortex. Intriguingly, FUS was also consistently observed at synaptic sites as detected by neuronal subcellular fractionation as well as by immunolabeling. To define a pre- and/or postsynaptic localization of FUS, we employed super-resolution fluorescence localization microscopy. FUS was found to be localized within the axon terminal in close proximity to the presynaptic vesicle protein Synaptophysin1 and adjacent to the active zone protein Bassoon, but well separated from the postsynaptic protein PSD-95. Having shown the presynaptic localization of FUS in the nervous system, a novel extranuclear role of FUS at neuronal contact sites has to be considered. Since there is growing evidence that local presynaptic translation might also be an important mechanism for plasticity, FUS – like the fragile X mental retardation protein FMRP – might act as one of the presynaptic RNA-binding proteins regulating this machinery. Our observation of presynaptic FUS should foster further investigations to determine its role in neurodegenerative diseases such as ALS and FTD.

Highlights

During the last decade a growing number of RNA-binding proteins has been identified as key players in the pathogenesis of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD)
Fused in Sarcoma (FUS) may play an additional role in synapse formation or function
another RNA-binding protein localized in the presynaptic compartment

Summary

Introduction

During the last decade a growing number of RNA-binding proteins has been identified as key players in the pathogenesis of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Both diseases are considered to be tightly linked by common clinical as well as pathophysiological hallmarks. FTD is the second most common form of early onset dementia leading to aggravating changes in personality and language It is characterized by progressive neuronal loss in frontal and temporal lobes. In 2006, the RNA-binding protein TDP-43 encoded by the TARDBP gene was identified as a major component of ubiquitinated aggregates in ALS and FTD (Arai et al, 2006; Neumann et al, 2006). While pathologic FUS aggregates in ALS only occur in the presence of FUS mutations, no FUS mutations have been reported in FTD cases with FUS pathology

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