Amyotrophic lateral sclerosis (ALS) is curable!
Widespread FUS mislocalization is a molecular hallmark of amyotrophic lateral sclerosis
In summary, we report widespread mislocalization of the FUS protein in ALS and propose a putative underlying mechanism for this process. FUS aggregation is a recognized feature of FUS mutation-related ALS. However, the concept that wild-type FUS nuclear-to-cytoplasmic mislocalization might be a more widespread feature of other forms of ALS has not been systematically assessed to our knowledge. Here we systematically investigated FUS protein localization across a human induced pluripotent stem cell model, mouse transgenic models and human post-mortem tissue from multiple cases of sporadic ALS. We find that the nuclear-to-cytoplasmic mislocalization of FUS is a more widespread feature of ALS than previously recognized.
Using linear mixed model analysis that accounts for inter-animal variation we showed that although FUS remained within the nucleus in the SOD1 mouse model , nuclear-to-cytoplasmic mislocalization abounded in the VCP mouse model, with a reduction in FUS nuclear to cytoplasmic ratio of −4.0176 1.1775. Nuclear-to-cytoplasmic mislocalization of FUS in human sporadic ALS. Having established that FUS is mislocalized in VCP-related ALS models, but not in SOD1, we next sought to address the generalizability of this finding across sporadic forms of ALS. To this end, we examined post-mortem spinal cord tissue from 12 sporadic ALS cases and eight healthy controls. We found clear evidence of nuclear-to-cytoplasmic FUS mislocalization in these sporadic ALS cases, but in the absence of cytoplasmic FUS inclusions.
Having found clear evidence that FUS nuclear-to-cytoplasmic mislocalization is more widespread in ALS than previously recognized, we sought to understand its molecular interplay with 167 aberrant intron retaining transcripts that we recently described in ALS. To this end we analysed iCLIP data, which allowed identification of RNA binding targets of the FUS protein. The core finding of our study is that the FUS protein is mislocalized from the nucleus to the cytoplasm in cases beyond FUS mutation-related ALS. Specifically, we find FUS mislocalization in VCP mutation-related ALS and, crucially, in sporadic ALS. Our findings have been carefully cross-validated in iPSC lines, a mouse transgenic model, and post-mortem tissue.
The pervasive mislocalization of FUS has likely evaded detection thus far as FUS largely remains unaggregated in the cytoplasm, rather than forming part of the TDP-43 aggregates in sporadic ALS cases. Our analysis of iCLIP data suggest that FUS binds avidly to the aberrantly retained intron of the SFPQ transcript in ALS. Cumulatively, our data are consistent with a working hypothesis that wild-type FUS might travel out of the nucleus when bound to the aberrantly retained intron 9 of the SFPQ transcript in ALS, though confirmation of such a mechanism will require detailed molecular follow-up work. The absence of FUS mislocalization in this context, together with the lack of TDP-43 proteinopathy, seems to further substantiate a recognized pathological divergence between SOD1-ALS and other forms of familial and sporadic ALS. In summary, we report a previously unrecognized widespread mislocalization of FUS in ALS, and propose a putative context-specific mechanism for this through its interaction with the ALS-related aberrantly retained intron 9 in SFPQ transcripts.
Mutations in FUS, an RNA processing protein, cause familial amyotrophic lateral sclerosis type 6.
Quantitative Susceptibility Mapping of the Motor Cortex in Amyotrophic Lateral Sclerosis and Primary Lateral Sclerosis
To overcome noise amplifications in the deconvolution, we used the morphology-enabled dipole inversion method for QSM reconstruction [13-15]. Qualitative Analysis Two neuroradiologists who were blinded to the presence or absence of MND performed qualitative scoring of the following four imaging features: motor cortex T2 hypointensity, motor cortex T2* hypointensity, motor cortex QSM hyperintensity, and corticospinal tract T2 hyperintensity. In our experience, in patients without motor cortex abnormalities, the motor cortex is slightly more hyperintense than the rest of the supratentorial cortex on QSM images. Scores for motor cortex QSM hyperintensity were assigned by each neuroradiologist as follows: 0, slightly more hyperintense than sensory cortex; 1, moderately more hyperintense than sensory cortex; or 2, markedly more hyperintense than sensory cortex. Relative susceptibility was calculated by subtraction of adjacent susceptibility from motor cortex susceptibility.
For the quantitative analysis, the mean relative motor cortex susceptibility of the right- and left-hand lobules was calculated for each patient. The highest diagnostic accuracy was achieved when the two observers used QSM and counted either moderately or markedly more hyperintense motor cortex compared with sensory cortex as positive for MND. QSM, which showed markedly more hyper-intensity in the motor than the sensory cortex, and T2-weighted FLAIR imaging, which showed corticospinal tract T2 hyperintensity, had the highest specificity. In the quantitative analysis, the 16 patients with MND had significantly greater relative motor cortex susceptibility than the 23 control patients. The optimal cutoff value for relative motor cortex susceptibility was found to be 40.5 ppb, which yielded a sensitivity of 87.5% and a specificity of 87.0%.
View larger versionFigure S5 shows correlations between mean relative motor cortex susceptibility and clinical measures of disease severity. Quantitatively, patients with ALS and PLS had statistically significantly greater relative motor cortex susceptibility than control patients, likely because of iron deposition, as found in a previous pathologic examination of the motor cortexes of ALS patients. Other than the patient with the greatest motor cortex susceptibility of 81.7 ppb and the patient with the lowest susceptibility of 17.1 ppb, the patients with upper MND were predominantly clustered between relative motor cortex susceptibility values of 41 and 48 ppb. These potential confounding factors should be considered in future studies in which an attempt is made to establish a relative motor cortex susceptibility cutoff for the diagnoses of ALS and PLS. The findings from our case-control study require further validation in a larger-scale prospective cohort study to determine whether QSM of the motor cortex can aid in the early diagnosis of MND and serve as an
imaging biomarker of disease severity.
Our aim was to investigate QSM of the motor cortex as a potential quantitative bio-marker in the diagnosis of ALS and PLS. In this case-control study, patients with ALS or PLS were found to have significantly greater relative motor cortex susceptibility than control patients, likely because of accelerated iron deposition.