A Nonerythroid Isoform of Protein 4.1R Interacts with Components of the Contractile Apparatus in Skeletal Myofibers

The ∼80-kDa erythroid 4.1R protein is a major component of the erythrocyte cytoskeleton, where it links transmembrane proteins to the underlying spectrin/actin complexes. A diverse collection of 4.1R isoforms has been described in nonerythroid cells, ranging from ∼30 to ∼210 kDa. In the current study, we identified the number and primary structure of 4.1R isoforms expressed in adult skeletal muscle and characterized the localization patterns of 4.1R message and protein. Skeletal muscle 4.1R appears to originate solely from the upstream translation initiation codon (AUG-1) residing in exon 2′. Combinations of alternatively spliced downstream exons generate an array of distinct 4.1R spliceoforms. Two major isoform classes of ∼105/110 and ∼135 kDa are present in muscle homogenates. 4.1R transcripts are distributed in highly ordered signal stripes, whereas 4.1R protein(s) decorate the sarcoplasm in transverse striations that are in register with A-bands. An ∼105/110-kDa 4.1R isoform appears to occur in vivo in a supramolecular complex with major sarcomeric proteins, including myosin, α-actin, and α-tropomyosin. In vitro binding assays showed that 4.1R may interact directly with the aforementioned contractile proteins through its 10-kDa domain. All of these observations suggest a topological model whereby 4.1R may play a scaffolding role by anchoring the actomyosin myofilaments and possibly modulating their displacements during contraction/relaxation.

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Molecular Targets of Androgen Signaling that Characterize Skeletal Muscle Recovery and Regeneration

Nuclear Receptor Signaling ◽

10.1621/nrs.13005 ◽

2015 ◽

Vol 13 (1) ◽

pp. nrs.13005 ◽

Cited By ~ 11

Author(s):

James G. MacKrell ◽

Benjamin C. Yaden ◽

Heather Bullock ◽

Keyue Chen ◽

Pamela Shetler ◽

...

Keyword(s):

Skeletal Muscle ◽

Molecular Targets ◽

Gene Signature ◽

Muscle Recovery ◽

In Vivo Models ◽

Adult Skeletal Muscle ◽

Injury Model ◽

Androgen Regulation

The high regenerative capacity of adult skeletal muscle relies on a self-renewing depot of adult stem cells, termed muscle satellite cells (MSCs). Androgens, known mediators of overall body composition and specifically skeletal muscle mass, have been shown to regulate MSCs. The possible overlapping function of androgen regulation of muscle growth and MSC activation has not been carefully investigated with regards to muscle regeneration. Therefore, the aim of this study was to examine coinciding androgen-mediated genetic changes in an in vitro MSC model and clinically relevant in vivo models. A gene signature was established via microarray analysis for androgen-mediated MSC engagement and highlighted several markers including follistatin (FST), IGF-1, C-X-C chemokine receptor 4 (CXCR4), hepatocyte growth factor (HGF) and glucocorticoid receptor (GR/Nr3c1). In an in vivo muscle atrophy model, androgen re-supplementation significantly increased muscle size and expression of IGF-1, FST, and HGF, while significantly decreasing expression of GR. Biphasic gene expression profiles over the 7-day re-supplementation period identifed temporal androgen regulation of molecular targets involved in satellite cell engagement into myogenesis. In a muscle injury model, removal of androgens resulted in delayed muscle recovery and regeneration. Modifications in the androgen signaling gene signature, along with reduced Pax7 and MyoD expression, suggested that limited MSC activation and increased inflammation contributed to the delayed regeneration. However, enhanced MSC activation in the androgen-deplete mouse injury model was driven by an androgen receptor (AR) agonist. These results provide novel in vitro and in vivo evidence describing molecular targets of androgen signaling, while also increasing support for translational use of AR agonists in skeletal muscle recovery and regeneration.

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FGF-2–dependent signaling activated in aged human skeletal muscle promotes intramuscular adipogenesis

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.2021013118 ◽

2021 ◽

Vol 118 (37) ◽

pp. e2021013118 ◽

Cited By ~ 1

Author(s):

Sebastian Mathes ◽

Alexandra Fahrner ◽

Umesh Ghoshdastider ◽

Hannes A. Rüdiger ◽

Michael Leunig ◽

...

Keyword(s):

Skeletal Muscle ◽

Transcriptional Activation ◽

Human Skeletal Muscle ◽

Muscle Growth ◽

Muscle Cells ◽

Adeno Associated Virus ◽

Adult Skeletal Muscle

Aged skeletal muscle is markedly affected by fatty muscle infiltration, and strategies to reduce the occurrence of intramuscular adipocytes are urgently needed. Here, we show that fibroblast growth factor-2 (FGF-2) not only stimulates muscle growth but also promotes intramuscular adipogenesis. Using multiple screening assays upstream and downstream of microRNA (miR)-29a signaling, we located the secreted protein and adipogenic inhibitor SPARC to an FGF-2 signaling pathway that is conserved between skeletal muscle cells from mice and humans and that is activated in skeletal muscle of aged mice and humans. FGF-2 induces the miR-29a/SPARC axis through transcriptional activation of FRA-1, which binds and activates an evolutionary conserved AP-1 site element proximal in the miR-29a promoter. Genetic deletions in muscle cells and adeno-associated virus–mediated overexpression of FGF-2 or SPARC in mouse skeletal muscle revealed that this axis regulates differentiation of fibro/adipogenic progenitors in vitro and intramuscular adipose tissue (IMAT) formation in vivo. Skeletal muscle from human donors aged >75 y versus <55 y showed activation of FGF-2–dependent signaling and increased IMAT. Thus, our data highlights a disparate role of FGF-2 in adult skeletal muscle and reveals a pathway to combat fat accumulation in aged human skeletal muscle.

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Thrombospondin-4, an extracellular matrix protein expressed in the developing and adult nervous system promotes neurite outgrowth.

The Journal of Cell Biology ◽

10.1083/jcb.131.4.1083 ◽

1995 ◽

Vol 131 (4) ◽

pp. 1083-1094 ◽

Cited By ~ 102

Author(s):

S Arber ◽

P Caroni

Keyword(s):

Skeletal Muscle ◽

Extracellular Matrix ◽

Nervous System ◽

Neuromuscular Junction ◽

Neurite Outgrowth ◽

Adult Skeletal Muscle ◽

Wide Range ◽

Thrombospondin 4

Extracellular matrix (ECM) molecules are involved in multiple aspects of cell-to-cell signaling during development and in the adult. In nervous system development, specific recognition processes, e.g., during axonal pathfinding and synaptogenesis involve modulation and signaling by ECM components. Much less is known about their presence and possible roles in the adult nervous system. We now report that thrombospondin-4 (TSP-4), a recently discovered member of the TSP gene family is expressed by neurons, promotes neurite outgrowth, and accumulates at the neuromuscular junction and at certain synapse-rich structures in the adult. To search for muscle genes that may be involved in neuromuscular signaling, we isolated cDNAs induced in adult skeletal muscle by denervation. One of these cDNAs coded for the rat homologue of TSP-4. In skeletal muscle, it was expressed by muscle interstitial cells. The transcript was further detected in heart and in the developing and adult nervous system, where it was expressed by a wide range of neurons. An antiserum to the unique carboxyl-terminal end of the protein allowed to specifically detect TSP-4 in transfected cells in vitro and on cryostat sections in situ. TSP-4 associated with ECM structures in vitro and in vivo. In the adult, it accumulated at the neuromuscular junction and at synapse-rich structures in the cerebellum and retina. To analyze possible activities of TSP-4 towards neurons, we carried out coculture experiments with stably transfected COS cells and motor, sensory, or retina neurons. These experiments revealed that TSP-4 was a preferred substrate for these neurons, and promoted neurite outgrowth. The results establish TSP-4 as a neuronal ECM protein associated with certain synapse-rich structures in the adult. Its activity towards embryonic neurons in vitro and its distribution in vivo suggest that it may be involved in local signaling in the developing and adult nervous system.

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Fibro-adipogenic progenitors of dystrophic mice are insensitive to NOTCH regulation of adipogenesis

Life Science Alliance ◽

10.26508/lsa.201900437 ◽

2019 ◽

Vol 2 (3) ◽

pp. e201900437 ◽

Cited By ~ 13

Author(s):

Milica Marinkovic ◽

Claudia Fuoco ◽

Francesca Sacco ◽

Andrea Cerquone Perpetuini ◽

Giulio Giuliani ◽

...

Keyword(s):

Skeletal Muscle ◽

Control Mechanism ◽

Notch Pathway ◽

Skeletal Muscle Regeneration ◽

Wild Type ◽

Adult Skeletal Muscle ◽

Pathological Conditions ◽

Dystrophic Mice

Fibro-adipogenic progenitors (FAPs) promote satellite cell differentiation in adult skeletal muscle regeneration. However, in pathological conditions, FAPs are responsible for fibrosis and fatty infiltrations. Here we show that the NOTCH pathway negatively modulates FAP differentiation both in vitro and in vivo. However, FAPs isolated from young dystrophin-deficient mdx mice are insensitive to this control mechanism. An unbiased mass spectrometry–based proteomic analysis of FAPs from muscles of wild-type and mdx mice suggested that the synergistic cooperation between NOTCH and inflammatory signals controls FAP differentiation. Remarkably, we demonstrated that factors released by hematopoietic cells restore the sensitivity to NOTCH adipogenic inhibition in mdx FAPs. These results offer a basis for rationalizing pathological ectopic fat infiltrations in skeletal muscle and may suggest new therapeutic strategies to mitigate the detrimental effects of fat depositions in muscles of dystrophic patients.

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Tristetraprolin and LPS-inducible CXC chemokine are rapidly induced in presumptive satellite cells in response to skeletal muscle injury

Journal of Cell Science ◽

10.1242/jcs.115.13.2701 ◽

2002 ◽

Vol 115 (13) ◽

pp. 2701-2712 ◽

Cited By ~ 4

Author(s):

Chetana Sachidanandan ◽

Ramkumar Sambasivan ◽

Jyotsna Dhawan

Keyword(s):

Skeletal Muscle ◽

Satellite Cells ◽

Cell Biology ◽

Muscle Injury ◽

Rna Binding ◽

C2c12 Myoblasts ◽

Adult Skeletal Muscle ◽

Cxc Chemokine

Myogenic precursor cells known as satellite cells persist in adult skeletal muscle and are responsible for its ability to regenerate after injury. Quiescent satellite cells are activated by signals emanating from damaged muscle. Here we describe the rapid activation of two genes in response to muscle injury; these transcripts encode LPS-inducible CXC chemokine (LIX), a neutrophil chemoattractant, and Tristetraprolin (TTP), an RNA-binding protein implicated in the regulation of cytokine expression. Using a synchronized cell culture model we show that C2C12 myoblasts arrested in G0 exhibit some molecular attributes of satellite cells in vivo: suppression of MyoD and Myf5 expression during G0 and their reactivation in G1. Synchronization also revealed cell cycle dependent expression of CD34, M-cadherin, HGF and PEA3, genes implicated in satellite cell biology. To identify other genes induced in synchronized C2C12 myoblasts we used differential display PCR and isolated LIX and TTP cDNAs. Both LIX and TTP mRNAs are short-lived, encode molecules implicated in inflammation and are transiently induced during growth activation in vitro. Further, LIX and TTP are rapidly induced in response to muscle damage in vivo. TTP expression precedes that of MyoD and is detected 30 minutes after injury. The spatial distribution of LIX and TTP transcripts in injured muscle suggests expression by satellite cells. Our studies suggest that in addition to generating new cells for repair, activated satellite cells may be a source of signaling molecules involved in tissue remodeling during regeneration.

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Skeletal muscle fibro-adipogenic progenitors of dystrophic mice are insensitive to NOTCH-dependent regulation of adipogenesis

10.1101/223370 ◽

2017 ◽

Cited By ~ 1

Author(s):

Milica Marinkovic ◽

Francesca Sacco ◽

Filomena Spada ◽

Lucia Lisa Petrilli ◽

Claudia Fuoco ◽

...

Keyword(s):

Skeletal Muscle ◽

Cell Mass ◽

Notch Pathway ◽

Notch Signaling Pathway ◽

Skeletal Muscle Regeneration ◽

Mdx Mice ◽

List Type ◽

Adult Skeletal Muscle

SummaryFibro adipogenic progenitors (FAPs) promote satellite cell differentiation in adult skeletal muscle regeneration. However, in pathological conditions, FAPs are responsible for fibrosis and fat infiltrations. Here we show that the NOTCH pathway negatively modulates FAP differentiation both in vitro and in vivo. However, FAPs isolated from young dystrophin-deficient mdx mice are insensitive to this control mechanism. Nonetheless, factors released by hematopoietic cells restore the sensitivity to NOTCH adipogenic inhibition. An unbiased mass spectrometry-based proteomic analysis of FAPs from muscles of wild type and mdx mice, revealed that the synergistic cooperation between NOTCH and inflammatory signals controls FAP differentiation. These results offer a basis for rationalizing the pathological outcomes of fat infiltrations in skeletal muscle and may suggest new therapeutic strategies to mitigate the detrimental effects of fatty depositions in muscles of dystrophic patients.HighlightsSingle-cell mass cytometry reveals that wt and mdx FAPs are in different cell states.Activation of the NOTCH signaling pathway negatively regulates adipogenesis of wt but not mdx FAPs.Deep proteomics suggests a mechanism explaining the different sensitivity of mdx- FAPs to NOTCH.TNF-a stimulation restores the anti-adipogenic effect of NOTCH in mdx FAPs.

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An alternative non-tyrosine protein kinase product of the c-src gene in chicken skeletal muscle

Molecular and Cellular Biology ◽

10.1128/mcb.10.8.4068-4079.1990 ◽

1990 ◽

Vol 10 (8) ◽

pp. 4068-4079

Author(s):

T Dorai ◽

L H Wang

Keyword(s):

Skeletal Muscle ◽

Kinase Domain ◽

Specific Protein ◽

Protein Product ◽

Upstream Region ◽

Tyrosine Kinase Domain ◽

Adult Skeletal Muscle ◽

Src Gene

While the c-src locus is expressed as a 4.0-kilobase (kb) mRNA coding for pp60c-src in various chicken tissues, including embryonic muscle, it is expressed as a novel 3.0-kb mRNA in adult skeletal muscle. We have analyzed the primary structure of this alternatively transcribed and spliced c-src mRNA. The sequence revealed three open reading frames, with the previously defined c-src exons 1 through 5 or 6 comprising the third, on the 3' untranslated region of this 3-kb mRNA. The exons coding for the tyrosine kinase domain of pp60c-src were excluded. On the 5' side, 2 kb of sequence upstream from the previously defined exon 1 of the c-src gene was included in this mRNA. The start site for the 3-kb mRNA probably lies downstream of that for the 4-kb mRNA. The first reading frame of the 3.0-kb mRNA, called sur (for src upstream region), encoded a 24-kilodalton (kDa) protein product rich in cysteine and proline residues. In vitro analysis indicated that the 24-kDa sur protein was membrane associated. Antibodies to sur protein detected in vivo a 24-kDa muscle-specific protein which was developmentally regulated and corresponded to the switch from the 4-kb to the 3-kb c-src mRNA. A striking kinetic pattern of appearance of sur protein and disappearance of pp60c-src suggests that the expression of these two proteins is inversely related.

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mTORC2 affects the maintenance of the muscle stem cell pool

Skeletal Muscle ◽

10.1186/s13395-019-0217-y ◽

2019 ◽

Vol 9 (1) ◽

Cited By ~ 1

Author(s):

Nathalie Rion ◽

Perrine Castets ◽

Shuo Lin ◽

Leonie Enderle ◽

Judith R. Reinhard ◽

...

Keyword(s):

Skeletal Muscle ◽

Mammalian Target Of Rapamycin ◽

Adult Skeletal Muscle ◽

Muscle Stem Cells ◽

And Function ◽

Muscle Homeostasis ◽

Biological Methods

Abstract Background The mammalian target of rapamycin complex 2 (mTORC2), containing the essential protein rictor, regulates cellular metabolism and cytoskeletal organization by phosphorylating protein kinases, such as PKB/Akt, PKC, and SGK. Inactivation of mTORC2 signaling in adult skeletal muscle affects its metabolism, but not muscle morphology and function. However, the role of mTORC2 in adult muscle stem cells (MuSCs) has not been investigated. Method Using histological, biochemical, and molecular biological methods, we characterized the muscle phenotype of mice depleted for rictor in the Myf5-lineage (RImyfKO) and of mice depleted for rictor in skeletal muscle fibers (RImKO). The proliferative and myogenic potential of MuSCs was analyzed upon cardiotoxin-induced injury in vivo and in isolated myofibers in vitro. Results Skeletal muscle of young and 14-month-old RImyfKO mice appeared normal in composition and function. MuSCs from young RImyfKO mice exhibited a similar capacity to proliferate, differentiate, and fuse as controls. In contrast, the number of MuSCs was lower in young RImyfKO mice than in controls after two consecutive rounds of cardiotoxin-induced muscle regeneration. Similarly, the number of MuSCs in RImyfKO mice decreased with age, which correlated with a decline in the regenerative capacity of mutant muscle. Interestingly, reduction in the number of MuSCs was also observed in 14-month-old RImKO muscle. Conclusions Our study shows that mTORC2 signaling is dispensable for myofiber formation, but contributes to the homeostasis of MuSCs. Loss of mTORC2 does not affect their myogenic function, but impairs the replenishment of MuSCs after repeated injuries and their maintenance during aging. These results point to an important role of mTORC2 signaling in MuSC for muscle homeostasis.

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An alternative non-tyrosine protein kinase product of the c-src gene in chicken skeletal muscle.

Molecular and Cellular Biology ◽

10.1128/mcb.10.8.4068 ◽

1990 ◽

Vol 10 (8) ◽

pp. 4068-4079 ◽

Cited By ~ 7

Author(s):

T Dorai ◽

L H Wang

Keyword(s):

Skeletal Muscle ◽

Kinase Domain ◽

Specific Protein ◽

Protein Product ◽

Upstream Region ◽

Tyrosine Kinase Domain ◽

Adult Skeletal Muscle ◽

Src Gene

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Lactate Metabolism and Satellite Cell Fate

Frontiers in Physiology ◽

10.3389/fphys.2020.610983 ◽

2020 ◽

Vol 11 ◽

Author(s):

Minas Nalbandian ◽

Zsolt Radak ◽

Masaki Takeda

Keyword(s):

Skeletal Muscle ◽

Cell Fate ◽

Cell Communication ◽

Cell Types ◽

Short Review ◽

Skeletal Muscle Regeneration ◽

Metabolic Switch ◽

Adult Skeletal Muscle

Lactate is one of the metabolic products of glycolysis. It is widely accepted as an important energy source for many cell types and more recently has been proposed to actively participate in cell-cell communication. Satellite cells (SCs), which are adult skeletal muscle stem cells, are the main players of the skeletal muscle regeneration process. Recent studies have proposed a metabolic switch to increase glycolysis in activated SCs. Moreover, lactate has been shown to affect SCs and myoblasts in vivo and in vitro. In this short review, we describe how metabolic variations relate with SC fate (quiescence, activation, proliferation, migration, differentiation, fusion, and self-renewal), as well as discuss possible relationships between lactate as a metabolite and as a signaling molecule affecting SC fate.

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