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Muscle-secreted neurturin couples myofiber oxidative metabolism and slow motor neuron identity

ABSTRACT: Endurance exercise promotes skeletal muscle vascularization, oxidative metabolism, fiber-type switching, and neuromuscular junction integrity. Importantly, the metabolic and contractile properties of the muscle fiber must be coupled to the identity of the innervating motor neuron (MN). Here, we show that muscle-derived neurturin (NRTN) acts on muscle fibers and MNs to couple their characteristics. Using a muscle-specific NRTN transgenic mouse (HSA-NRTN) and RNA-sequencing of MN somas, we observed that retrograde NRTN signaling promotes a shift towards a slow MN identity. In muscle, NRTN increased capillary density, oxidative capacity, and induced a transcriptional reprograming favoring fatty acid metabolism over glycolysis. This combination of effects on muscle and MNs, makes HSA-NRTN mice lean with remarkable exercise performance and motor coordination. Interestingly, HSA-NRTN mice largely recapitulate the phenotype of mice with muscle-specific expression of its upstream regulator PGC-1ɑ1. This work identifies NRTN as a myokine that couples muscle oxidative capacity to slow MN identity.

ORGANISM(S): Mus musculus

PROVIDER: GSE180266 | GEO | 2021/11/30

REPOSITORIES: GEO

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Project description:Motor neuron (MN), together with interneuron, are the two major neuronal types in spinal cord. MNs control muscle movement and are essential for breathing, walking and fine motor skills. Malfunction of MNs is frequently associated with neuronal diseases such as spinal muscular atrophy and amyotrophic lateral sclerosis. To establish normal function, MNs need to be differentiated properly from neural progenitor cells. Thus, it is of great importance to study the mechanism for MN specification. This study focuses on Mnx1 - a conserved homeobox transcription factor gets expressed during MN specification. Mnx1 is also the most widely used MN marker. Previous studies reported that Mnx1 mutation in mouse causes early lethality - probably by affecting the controlling over respiratory system. However, the exact role of Mnx1 for MN identity remains poorly understood. Taking advantage of a recently developed in vitro model for efficient MN induction from mouse ES cells, we combined experimental and OMICs techniques to systematically investigate the molecular function of Mnx1. We identified thousands of Mnx1 binding sites - many are co-bound by core MN factor Lhx3 and Isl1 and lack active histone marks. Disruption of Mnx1 causes increased expression of 85 genes - while only 14 genes get down-regulated. Up-regulated genes are enriched with neuronal functions, usually get expressed during MN differentiation, and tend to have higher expression in motor neurons and brain compared with other tissues – indicating Mnx1 may fine tune neuronal genes to desired level. However, only a dozen of regions with increased H3K27ac marks are bound by Mnx1, and only two up-regulated genes (Pbx3 and Pou6f2) are identified as putative direct targets of Mnx1 - both are core neuronal factors with the potential to regulate other differential neuronal genes. These results suggest that Mnx1 may contribute to MN identity by fine-tuning the expression of many neuronal genes through direct regulation of a few core neuronal transcription factors. In summary, this study represents the first systematic investigation about the molecular function of the core MN factor Mnx1. It clarifies the mechanism of Mnx1 for MN identity, and also improves the understanding about the regulation mode of homeobox transcription factors.

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Muscle-secreted neurturin couples myofiber oxidative metabolism and slow motor neuron identity

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