- TDP-43 and RNA form amyloid-like myo-granules in regenerating muscle
- Targeted neurotechnology restores walking in humans with spinal cord injury
- DYNLL1 binds to MRE11 to limit DNA end resection in BRCA1-deficient cells
- Shared and distinct transcriptomic cell types across neocortical areas
- De novo NAD+ synthesis enhances mitochondrial function and improves health
1. TDP-43 and RNA form amyloid-like myo-granules in regenerating muscle
A dominant histopathological feature in neuromuscular diseases, including amyotrophic lateral sclerosis and inclusion body myopathy, is cytoplasmic aggregation of the RNA-binding protein TDP-43. Although rare mutations in TARDBP—the gene that encodes TDP-43—that lead to protein misfolding often cause protein aggregation, most patients do not have any mutations in TARDBP. Therefore, aggregates of wild-type TDP-43 arise in most patients by an unknown mechanism. Here Thomas O. Vogler at University of Colorado in Boulder, USA and his colleagues show that TDP-43 is an essential protein for normal skeletal muscle formation that unexpectedly forms cytoplasmic, amyloid-like oligomeric assemblies, which they call myo-granules, during regeneration of skeletal muscle in mice and humans. Myo-granules bind to mRNAs that encode sarcomeric proteins and are cleared as myofibres mature. Although myo-granules occur during normal skeletal-muscle regeneration, myo-granules can seed TDP-43 amyloid fibrils in vitro and are increased in a mouse model of inclusion body myopathy. Therefore, increased assembly or decreased clearance of functionally normal myo-granules could be the source of cytoplasmic TDP-43 aggregates that commonly occur in neuromuscular disease.
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2. Targeted neurotechnology restores walking in humans with spinal cord injury
Spinal cord injury leads to severe locomotor deficits or even complete leg paralysis. Here Fabien B. Wagner at Swiss Federal Institute of Technology (EPFL) in Lausanne, Switzerland and his colleagues introduce targeted spinal cord stimulation neurotechnologies that enabled voluntary control of walking in individuals who had sustained a spinal cord injury more than four years ago and presented with permanent motor deficits or complete paralysis despite extensive rehabilitation. Using an implanted pulse generator with real-time triggering capabilities, they delivered trains of spatially selective stimulation to the lumbosacral spinal cord with timing that coincided with the intended movement. Within one week, this spatiotemporal stimulation had re-established adaptive control of paralysed muscles during overground walking. Locomotor performance improved during rehabilitation. After a few months, participants regained voluntary control over previously paralysed muscles without stimulation and could walk or cycle in ecological settings during spatiotemporal stimulation. These results establish a technological framework for improving neurological recovery and supporting the activities of daily living after spinal cord injury.
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3. DYNLL1 binds to MRE11 to limit DNA end resection in BRCA1-deficient cells
Limited DNA end resection is the key to impaired homologous recombination in BRCA1-mutant cancer cells. Here, using a loss-of-function CRISPR screen, Yizhou Joseph He at Harvard Medical School in Boston, USA and his colleagues identify DYNLL1 as an inhibitor of DNA end resection. The loss of DYNLL1 enables DNA end resection and restores homologous recombination in BRCA1-mutant cells, thereby inducing resistance to platinum drugs and inhibitors of poly(ADP-ribose) polymerase. Low BRCA1 expression correlates with increased chromosomal aberrations in primary ovarian carcinomas, and the junction sequences of somatic structural variants indicate diminished homologous recombination. Concurrent decreases in DYNLL1 expression in carcinomas with low BRCA1 expression reduced genomic alterations and increased homology at lesions. In cells, DYNLL1 limits nucleolytic degradation of DNA ends by associating with the DNA end-resection machinery (MRN complex, BLM helicase and DNA2 endonuclease). In vitro, DYNLL1 binds directly to MRE11 to limit its end-resection activity. Therefore, they infer that DYNLL1 is an important anti-resection factor that influences genomic stability and responses to DNA-damaging chemotherapy.
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4. Shared and distinct transcriptomic cell types across neocortical areas
The neocortex contains a multitude of cell types that are segregated into layers and functionally distinct areas. To investigate the diversity of cell types across the mouse neocortex, here Bosiljka Tasic at Allen Institute for Brain Science in Seattle, USA and his colleagues analysed 23,822 cells from two areas at distant poles of the mouse neocortex: the primary visual cortex and the anterior lateral motor cortex. They define 133 transcriptomic cell types by deep, single-cell RNA sequencing. Nearly all types of GABA (γ-aminobutyric acid)-containing neurons are shared across both areas, whereas most types of glutamatergic neurons were found in one of the two areas. By combining single-cell RNA sequencing and retrograde labelling, they match transcriptomic types of glutamatergic neurons to their long-range projection specificity. Their study establishes a combined transcriptomic and projectional taxonomy of cortical cell types from functionally distinct areas of the adult mouse cortex.
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5. De novo NAD+ synthesis enhances mitochondrial function and improves health
Nicotinamide adenine dinucleotide (NAD+) is a co-substrate for several enzymes, including the sirtuin family of NAD+-dependent protein deacylases. Beneficial effects of increased NAD+ levels and sirtuin activation on mitochondrial homeostasis, organismal metabolism and lifespan have been established across species. Here Elena Katsyuba at École Polytechnique Fédérale de Lausanne in Lausanne, Switzerland and his colleagues show that α-amino-β-carboxymuconate-ε-semialdehyde decarboxylase (ACMSD), the enzyme that limits spontaneous cyclization of α-amino-β-carboxymuconate-ε-semialdehyde in the de novo NAD+ synthesis pathway, controls cellular NAD+ levels via an evolutionarily conserved mechanism in Caenorhabditis elegans and mouse. Genetic and pharmacological inhibition of ACMSD boosts de novo NAD+ synthesis and sirtuin 1 activity, ultimately enhancing mitochondrial function. They also characterize two potent and selective inhibitors of ACMSD. Because expression of ACMSD is largely restricted to kidney and liver, these inhibitors may have therapeutic potential for protection of these tissues from injury. In summary, they identify ACMSD as a key modulator of cellular NAD+ levels, sirtuin activity and mitochondrial homeostasis in kidney and liver.
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