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Deep proteome of aging skeletal muscles reveals Smoc2 as a modulator of satellite cell regenerative capacity

ABSTRACT: During aging, the number and functionality of muscle stem cells (MuSCs) decreases leading to impaired regeneration of aged skeletal muscle. In addition to intrinsic changes in aged MuSCs, extracellular matrix (ECM) proteins deriving from other cell types, e.g., fibrogenic-adipogenic progenitor cells (FAPs), contribute to the aging phenotype of MuSCs and impaired regeneration in the elderly. So far, no comprehensive analysis on how age-dependent changes in the whole skeletal muscle proteome affect MuSC function have been conducted. Here, we investigated age-dependent changes in the proteome of different skeletal muscle types by applying deep quantitative mass spectrometry. We identified 183 extracellular matrix proteins that show different abundances in skeletal muscles of old mice. By integrating single cell sequencing data, we reveal that transcripts of those ECM proteins are mainly expressed in FAPs, suggesting that FAPs are the main contributors to ECM remodelling during aging. We functionally investigated one of those ECM molecules, namely Smoc2, which is aberrantly expressed during aging. We show that Smoc2 levels are elevated during regeneration and that its accumulation in the aged MuSC niche causes impairment of MuSCs function through constant activation of integrin/MAPK signaling. In vivo, supplementation of exogenous Smoc2 hampers the regeneration of young muscles following serial injuries, leading to a phenotype reminiscent of regenerating aged skeletal muscle. Taken together, we provide a comprehensive resource of changes in the composition of the ECM of aged skeletal muscles, we pinpoint the cell types driving these changes, and we identify a new niche protein causing functional impairment of MuSCs thereby hampering the regeneration capacity of skeletal muscles.

INSTRUMENT(S): Orbitrap Fusion Lumos

ORGANISM(S): Mus Musculus (mouse)

TISSUE(S): Leg Muscle

SUBMITTER: Alessandro Ori

LAB HEAD: Alessandro Ori

PROVIDER: PXD015616 | Pride | 2021-11-25

REPOSITORIES: Pride

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Project description:Background: Skeletal muscle crucially depends on motor innervation, and, when damaged, on the resident muscle stem cells (MuSCs). However, the role and function of MuSCs in the context of denervation remains poorly understood. Methods: Alterations of MuSCs and their myofiber niche after denervation were investigated in a surgery-based mouse model of unilateral sciatic nerve transection. FACS-isolated MuSCs were subjected to RNA-sequencing and mass spectrometry for the analysis of intrinsic changes after denervation and in vivo assays, such as Cardiotoxin-induced muscle injury or MuSC transplantation, were performed to assess MuSC functions after denervation. Bioinformatic and histological analyses were conducted to further examine MuSCs and their myofiber niche after denervation. Results: Muscle cross section analysis revealed a significant increase in Pax7 (p-value= 0.0441), Pax7/Ki67 (p-value= 0.0023), MyoD (p-value= 0.0016) and Myog (p-value= 0.0057) positive cells after denervation, illustrating a break of quiescence and commitment to the myogenic lineage. An Omics approach showed profound intrinsic alterations on the mRNA (2613 differentially expressed genes, p-value <0.05) and protein (1096 differentially abundant proteins, q-value <0.05) level of MuSCs 21 days after denervation. Skeletal muscle injury together with denervation surgery caused deregulated regeneration, indicated by the reduced number of proliferating MuSCs and sustained high levels of developmental myosin heavy chain (Sham: 1 % vs DEN: 40 % of all myofibers), at 21 days post-surgery. In a transplantation assay, MuSCs from a denervated host were still able to engraft and fuse to form new myofibers, irrespective of the innervation status of the recipient muscle. Analysis of myofibers revealed not only massive changes in the expression profile (10492 differentially expressed genes, p-value <0.05) after denervation, but it was also shown that secretion of Opn and Tgfb1 from denervated myofibers was increased 30-fold and 6000-fold, respectively. Bioinformatic analyses indicated strong upregulation of gene expression of the transcription factor Junb in MuSCs from denervated muscles (log2 fold change = 3.27). Of interest, Tgfb1 recombinant protein was able to induce Junb gene expression in vitro, demonstrating that myofiber-secreted ligands can induce gene expression changes in MuSCs, which might result in the phenotypes observed after denervation. Conclusion: Skeletal muscle denervation is altering myofiber secretion, causing MuSC activation and profound intrinsic changes, leading to reduced regenerative capacity. As MuSCs possess a remarkable regenerative potential, they might represent a promising target for novel treatment options for neuromuscular disorders and peripheral nerve injuries.

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Deep proteome of aging skeletal muscles reveals Smoc2 as a modulator of satellite cell regenerative capacity

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