ALS-FUS mutations cause abnormal PARylation and histone H1.2 interaction, leading to pathological changes.

The majority of severe early-onset and juvenile cases of amyotrophic lateral sclerosis (ALS) are caused by mutations in the FUS gene, resulting in rapid disease progression. Mutant FUS accumulates within stress granules (SGs), thereby affecting the dynamics of these ribonucleoprotein complexes. Here, we define the interactome of the severe mutant FUSP525L variant in human induced pluripotent stem cell (iPSC)-derived motor neurons. We find increased interaction of FUSP525L with the PARP1 enzyme, promoting poly-ADP-ribosylation (PARylation) and binding of FUS to histone H1.2. Inhibiting PARylation or reducing H1.2 levels alleviates mutant FUS aggregation, SG alterations, and apoptosis in human motor neurons. Conversely, elevated H1.2 levels exacerbate FUS-ALS phenotypes, driven by the internally disordered terminal domains of H1.2. In C. elegans models, knockdown of H1.2 and PARP1 orthologs also decreases FUSP525L aggregation and neurodegeneration, whereas H1.2 overexpression worsens ALS-related changes. Our findings indicate a link between PARylation, H1.2, and FUS with potential therapeutic implications.

Cold temperature extends longevity and prevents disease-related protein aggregation through PA28γ-induced proteasomes.

Aging is a primary risk factor for neurodegenerative disorders that involve protein aggregation. Because lowering body temperature is one of the most effective mechanisms to extend longevity in both poikilotherms and homeotherms, a better understanding of cold-induced changes can lead to converging modifiers of pathological protein aggregation. Here, we find that cold temperature (15 °C) selectively induces the trypsin-like activity of the proteasome in Caenorhabditis elegans through PSME-3, the worm orthologue of human PA28γ/PSME3. This proteasome activator is required for cold-induced longevity and ameliorates age-related deficits in protein degradation. Moreover, cold-induced PA28γ/PSME-3 diminishes protein aggregation in C. elegans models of age-related diseases such as Huntington's and amyotrophic lateral sclerosis. Notably, exposure of human cells to moderate cold temperature (36 °C) also activates trypsin-like activity through PA28γ/PSME3, reducing disease-related protein aggregation and neurodegeneration. Together, our findings reveal a beneficial role of cold temperature that crosses evolutionary boundaries with potential implications for multi-disease prevention.

The intrinsic proteostasis network of stem cells.

The proteostasis network adjusts protein composition and maintains protein integrity, which are essential processes for cell function and viability. Current efforts, given their intrinsic characteristics, regenerative potential and fundamental biological functions, have been directed to define proteostasis of stem cells. These insights demonstrate that embryonic stem cells and induced pluripotent stem cells exhibit an endogenous proteostasis network that not only modulates their pluripotency and differentiation but also provides a striking ability to suppress aggregation of disease-related proteins. Moreover, recent findings establish a central role of enhanced proteostasis to prevent the aging of somatic stem cells in adult organisms. Notably, proteostasis is also required for the biological purpose of adult germline stem cells, that is to be passed from one generation to the next. Beyond these links between proteostasis and stem cell function, we also discuss the implications of these findings for disease, aging, and reproduction.

Modeling the Pathological Long-Range Regulatory Effects of Human Structural Variation with Patient-Specific hiPSCs.

The pathological consequences of structural variants disrupting 3D genome organization can be difficult to elucidate in vivo due to differences in gene dosage sensitivity between mice and humans. This is illustrated by branchiooculofacial syndrome (BOFS), a rare congenital disorder caused by heterozygous mutations within TFAP2A, a neural crest regulator for which humans, but not mice, are haploinsufficient. Here, we present a BOFS patient carrying a heterozygous inversion with one breakpoint located within a topologically associating domain (TAD) containing enhancers essential for TFAP2A expression in human neural crest cells (hNCCs). Using patient-specific hiPSCs, we show that, although the inversion shuffles the TFAP2A hNCC enhancers with novel genes within the same TAD, this does not result in enhancer adoption. Instead, the inversion disconnects one TFAP2A allele from its cognate enhancers, leading to monoallelic and haploinsufficient TFAP2A expression in patient hNCCs. Our work illustrates the power of hiPSC differentiation to unveil long-range pathomechanisms.