Jansen‐West, Karen

PolyQ ATXN3 is a pharmacodynamic marker for SCA3, and a SNP associated with the expanded allele may serve to specifically target mutant ATXN3 .

Abstract Background Self-assembly of the amyloid-β (Aβ) peptide into aggregates, from small oligomers to amyloid fibrils, is fundamentally linked with Alzheimer’s disease (AD). However it is clear that not all forms of Aβ are equally harmful, and that linking a specific aggregate to toxicity also depends on the assays and model systems used [1, 2]. Though a central postulate of the amyloid cascade hypothesis, there remain many gaps in our understanding regarding the links between Aβ deposition and neurodegeneration. Methods In this study, we examined familial mutations of Aβ that increase aggregation and oligomerization, E22G and DE22, and induce cerebral amyloid angiopathy, E22Q and D23N. We also investigated synthetic mutations that stabilize dimerization, S26C, and a phospho-mimetic, S8E, and non-phospho-mimetic, S8A. To that end, we utilized BRI2-Aβ fusion technology and rAAV2/1 based somatic brain transgenesis in mice to selectively express individual mutant Aβ species in vivo. In parallel we generated PhiC31-based transgenic Drosophila melanogaster expressing wild type (WT) and Aβ40 and Aβ42 mutants, fused to the Argos signal peptide to assess the extent of Aβ42-induced toxicity as well as to interrogate the combined effect of different Aβ40 and Aβ42 species.Results When expressed in the mouse brain for 6 months, Aβ42 E22G, Aβ42 E22Q/D23N, and Aβ42WT formed amyloid aggregates consisting of some diffuse material as well as cored plaques, whereas other mutants formed predominantly diffuse amyloid deposits. Moreover, while Aβ40WT showed no distinctive phenotype, Aβ40 E22G and E22Q/D23N formed unique aggregates that accumulated in mouse brains. This is the first evidence that mutant Aβ40 overexpression leads to deposition under certain conditions. Interestingly, we found that mutant Aβ42 E22G, E22Q, and S26C, but not Aβ40, were toxic to the eye of Drosophila. In contrast, flies expressing a copy of Aβ40 (WT or mutants) in addition to Aβ42WT, showed improved phenotypes, suggesting possible protective qualities for Aβ40. Conclusions These studies suggest that while some Aβ40 mutants form unique amyloid aggregates in mouse brains, they do not exacerbate Aβ42 toxicity in Drosophila, which highlights the significance of using different systems for a better understanding of AD pathogenicity and more accurate screening for new potential therapies.

Abstract BackgroundSelf-assembly of the amyloid-β (Aβ) peptide into aggregates, from small oligomers to amyloid fibrils, is fundamentally linked with Alzheimer’s disease (AD). However it is clear that not all forms of Aβ are equally harmful, and that linking a specific aggregate to toxicity also depends on the assays and model systems used [1, 2]. Though a central postulate of the amyloid cascade hypothesis, there remain many gaps in our understanding regarding the links between Aβ deposition and neurodegeneration.MethodsIn this study, we examined familial mutations of Aβ that increase aggregation and oligomerization, E22G and DE22, and induce cerebral amyloid angiopathy, E22Q and D23N. We also investigated synthetic mutations that stabilize dimerization, S26C, and a phospho-mimetic, S8E, and non-phospho-mimetic, S8A. To that end, we utilized BRI2-Aβ fusion technology and rAAV2/1 based somatic brain transgenesis in mice to selectively express individual mutant Aβ species in vivo . In parallel we generated PhiC31-based transgenic Drosophila melanogaster expressing wild type (WT) and Aβ40 and Aβ42 mutants, fused to the Argos signal peptide to assess the extent of Aβ42-induced toxicity as well as to interrogate the combined effect of different Aβ40 and Aβ42 species.ResultsWhen expressed in the mouse brain for 6 months, Aβ42 E22G, Aβ42 E22Q/D23N, and Aβ42WT formed amyloid aggregates consisting of some diffuse material as well as cored plaques, whereas other mutants formed predominantly diffuse amyloid deposits. Moreover, while Aβ40WT showed no distinctive phenotype, Aβ40 E22G and E22Q/D23N formed unique aggregates that accumulated in mouse brains. This is the first evidence that mutant Aβ40 overexpression leads to deposition under certain conditions. Interestingly, we found that mutant Aβ42 E22G, E22Q, and S26C, but not Aβ40, were toxic to the eye of Drosophila . In contrast, flies expressing a copy of Aβ40 (WT or mutants) in addition to Aβ42WT, showed improved phenotypes, suggesting possible protective qualities for Aβ40.ConclusionsThese studies suggest that some Aβ40 mutants form unique amyloid aggregates in mouse brains, despite protecting against Aβ42 toxicity in Drosophila , which highlights the significance of using different systems for a better understanding of AD pathogenicity and more accurate screening for new potential therapies.

G 4 C 2 repeat–derived poly(GR) plays a key role in mediating TDP-43 mislocalization and aggregation in vitro and in vivo.

Abstract BackgroundSelf-assembly of the amyloid-β (Aβ) peptide into aggregates, ranging from small oligomers to amyloid fibrils, is fundamentally linked with Alzheimer’s disease (AD). However it is clear that not all forms of Aβ are equally harmful, and that linking a specific aggregate to toxicity also depends on the assays and model systems used [1, 2]. Indeed, though a central postulate of the amyloid cascade hypothesis, there remain many gaps in our understanding regarding the links between Aβ deposition and neurodegeneration.MethodsIn this study we utilized BRI2-Aβ fusion technology and rAAV2/1 based somatic brain transgenesis to examine Aβ aggregates that form from selective expression of individual mutant Aβ species in vivo. In parallel we generated PhiC31-based transgenic Drosophila melanogaster expressing WT and mutant Aβ40 and Aβ42, fused to the Argos signal peptide and placed under the GAL4-upstream activation sequence (UAS) expression system in order to assess the extent of Aβ42-induced toxicity as well as to interrogate the combined effect of different forms of Aβ40 and Aβ42 species.ResultsWhen expressed in the mouse brain for 6 months, Aβ42 E22G, Aβ42 E22Q/D23N, and Aβ42 WT formed amyloid aggregates consisting of some diffuse material as well as cored plaques, whereas other mutants formed predominantly diffuse amyloid deposits. Moreover, while Aβ40WT showed no distinctive phenotype, Aβ40 E22G and E22Q/D23N formed unique aggregates that accumulated in mouse brains. This is the first evidence that mutant Aβ40 overexpression leads to deposition under certain conditions. Interestingly, we found that mutant Aβ42 E22G, E22Q, and S26C, but not Aβ40, were toxic to the eye of the flies and exacerbated their behavior. In contrast, flies expressing a copy of Aβ40 (wild type [WT] or mutants) in addition to Aβ42 WT, showed improved phenotypes, suggesting possible protective qualities for Aβ40.ConclusionsThese studies suggest that some Aβ40 mutants form unique amyloid aggregates in mouse brains, despite being protective against Aβ42 toxicity in Drosophila, which highlights the significance of using different systems for a better understanding of AD pathogenicity and more accurate screening for new potential therapies.

How dipeptide repeats cause pathology A repeat expansion in the chromosome 9 open reading frame 72 ( C9orf72 ) gene is the most common known cause of two neurodegenerative diseases: frontotemporal dementia and amyotrophic lateral sclerosis. This expansion leads to the abnormal production of proteins of repeating dipeptides, but their contribution to disease pathogenesis remains unclear. Zhang et al. engineered a mouse model to study the consequences of one of these dipeptides—prolinearginine dipeptide repeat protein, poly(PR)—in the brain. They found that poly(PR) caused neuron loss as well as motor and memory impairments. These detrimental effects resulted from poly(PR)-induced perturbation of heterochromatin function, a tightly packed form of DNA that represses gene expression. Science , this issue p. eaav2606

Poly(GP) proteins are a promising pharmacodynamic marker for developing and testing therapeutics for treating C9ORF72 -associated amyotrophic lateral sclerosis.

Targeting three defects with one strategy The neurodegenerative diseases amyotrophic lateral sclerosis and frontotemporal dementia are most commonly caused by a mutation in the C9orf72 gene. The mutation is an expanded hexanucleotide repeat in a noncoding region. The expanded repeat produces sense and antisense RNA transcripts, which accumulate in patient cells and appear to sequester RNA-binding proteins. The sense and antisense transcripts are also translated into dipeptide repeat proteins, which are aggregation-prone and accumulate in the brain and spinal cord. Last, loss of function from reduced expression of C9orf72 in neurons and glia could contribute to the disease. Kramer et al. targeted both sense and antisense repeats by blocking a single gene called SPT4 , which mitigated degeneration in human cells by reducing all three types of pathologies. Science , this issue p. 708