Low Level of Expression of C-Terminally Truncated Human FUS Causes Extensive Changes in the Spinal Cord Transcriptome of Asymptomatic Transgenic Mice

Abl kinase-mediated FUS Tyr526 phosphorylation alters nucleocytoplasmic FUS localization in FTLD-FUS

Nuclear to cytoplasmic mislocalization and aggregation of multiple RNA-binding proteins (RBPs), including FUS, are the main neuropathological features of the majority of cases of amyotrophic lateral sclerosis (ALS) and frontotemporal lobular degeneration (FTLD). In ALS-FUS, these aggregates arise from disease-associated mutations in FUS, whereas in FTLD-FUS, the cytoplasmic inclusions do not contain mutant FUS, suggesting different molecular mechanisms of FUS pathogenesis in FTLD that remain to be investigated. We have previously shown that phosphorylation of the C-terminal Tyr526 of FUS results in increased cytoplasmic retention of FUS due to impaired binding to the nuclear import receptor TNPO1. Inspired by the above notions, in the current study we developed a novel antibody against the C-terminally phosphorylated Tyr526 FUS (FUSp-Y526) that is specifically capable of recognizing phosphorylated cytoplasmic FUS, which is poorly recognized by other commercially available FUS antibodies. Using this FUSp-Y526 antibody, we demonstrated a FUS phosphorylation-specific effect on the cytoplasmic distribution of soluble and insoluble FUSp-Y526 in various cells and confirmed the involvement of the Src kinase family in Tyr526 FUS phosphorylation. In addition, we found that FUSp-Y526 expression pattern correlates with active pSrc/pAbl kinases in specific brain regions of mice, indicating preferential involvement of cAbl in the cytoplasmic mislocalization of FUSp-Y526 in cortical neurons. Finally, the pattern of immunoreactivity of active cAbl kinase and FUSp-Y526 revealed altered cytoplasmic distribution of FUSp-Y526 in cortical neurons of post-mortem frontal cortex tissue from FTLD patients compared with controls. The overlap of FUSp-Y526 and FUS signals was found preferentially in small diffuse inclusions and was absent in mature aggregates, suggesting possible involvement of FUSp-Y526 in the formation of early toxic FUS aggregates in the cytoplasm that are largely undetected by commercially available FUS antibodies. Given the overlapping patterns of cAbl activity and FUSp-Y526 distribution in cortical neurons, and cAbl induced sequestration of FUSp-Y526 into G3BP1 positive granules in stressed cells, we propose that cAbl kinase is actively involved in mediating cytoplasmic mislocalization and promoting toxic aggregation of wild-type FUS in the brains of FTLD patients, as a novel putative underlying mechanism of FTLD-FUS pathophysiology and progression.

A bioisostere of Dimebon/Latrepirdine delays the onset and slows the progression of pathology in FUS transgenic mice

Aims

To assess effects of DF402, a bioisostere of Dimebon/Latrepirdine, on the disease progression in the transgenic model of amyotrophic lateral sclerosis (ALS) caused by expression of pathogenic truncated form of human FUS protein.

Methods

Mice received DF402 from the age of 42 days and the onset of clinical signs, the disease duration and animal lifespan were monitored for experimental and control animals, and multiple parameters of their gait were assessed throughout the pre‐symptomatic stage using CatWalk system followed by a bioinformatic analysis. RNA‐seq was used to compare the spinal cord transcriptomes of wild‐type, untreated, and DF402‐treated FUS transgenic mice.

Results

DF402 delays the onset and slows the progression of pathology. We developed a CatWalk analysis protocol that allows detection of gait changes in FUS transgenic mice and the effect of DF402 on their gait already at early pre‐symptomatic stage. At this stage, a limited number of genes significantly change expression in transgenic mice and for 60% of these genes, DF402 treatment causes the reversion of the expression pattern.

Conclusion

DF402 slows down the disease progression in the mouse model of ALS, which is consistent with previously reported neuroprotective properties of Dimebon and its other bioisosteres. These results suggest that these structures can be considered as lead compounds for further optimization to obtain novel medicines that might be used as components of complex ALS therapy.

Neuro-Cells therapy improves motor outcomes and suppresses inflammation during experimental syndrome of amyotrophic lateral sclerosis in mice

Aims

Mutations in DNA/RNA‐binding factor (fused‐in‐sarcoma) FUS and superoxide dismutase‐1 (SOD‐1) cause amyotrophic lateral sclerosis (ALS). They were reproduced in SOD‐1‐G93A (SOD‐1) and new FUS[1‐359]‐transgenic (FUS‐tg) mice, where inflammation contributes to disease progression. The effects of standard disease therapy and anti‐inflammatory treatments were investigated using these mutants.

Methods

FUS‐tg mice or controls received either vehicle, or standard ALS treatment riluzole (8 mg/kg/day), or anti‐inflammatory drug a selective blocker of cyclooxygenase‐2 celecoxib (30 mg/kg/day) for six weeks, or a single intracerebroventricular (i.c.v.) infusion of Neuro‐Cells (a preparation of 1.39 × 10⁶ mesenchymal and hemopoietic human stem cells, containing 5 × 10⁵ of CD34⁺ cells), which showed anti‐inflammatory properties. SOD‐1 mice received i.c.v.‐administration of Neuro‐Cells or vehicle.

Results

All FUS‐tg‐treated animals displayed less marked reductions in weight gain, food/water intake, and motor deficits than FUS‐tg‐vehicle‐treated mice. Neuro‐Cell‐treated mutants had reduced muscle atrophy and lumbar motor neuron degeneration. This group but not celecoxib‐FUS‐tg‐treated mice had ameliorated motor performance and lumbar expression of microglial activation marker, ionized calcium‐binding adapter molecule‐1 (Iba‐1), and glycogen‐synthase‐kinase‐3ß (GSK‐3ß). The Neuro‐Cells‐treated‐SOD‐1 mice showed better motor functions than vehicle‐treated‐SOD‐1 group.

Conclusion

The neuropathology in FUS‐tg mice is sensitive to standard ALS treatments and Neuro‐Cells infusion. The latter improves motor outcomes in two ALS models possibly by suppressing microglial activation.