scholarly journals mTORC2 affects the maintenance of the muscle stem cell pool

2019 ◽  
Vol 9 (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.

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

2021 ◽  
Vol 118 (37) ◽  
pp. e2021013118 ◽  
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.

scholarly journals The Generation and Regulation of Tissue-Resident Tregs and Their Role in Autoimmune Diseases

2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Shuang Wang ◽  
Xueyang Zou ◽  
Yi Zhang ◽  
Xiaoya Wang ◽  
Wei Yang ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
T Cells ◽  
Immune Responses ◽  
Autoimmune Diseases ◽  
Hot Spot ◽  
Exploratory Stage ◽  
And Function

Regulatory T cells (Tregs), as an important subset of T cells, play an important role in maintaining body homeostasis by regulating immune responses and preventing autoimmune diseases. In-depth research finds that Tregs have strong instability and plasticity, and according to their developmental origin, Tregs can be classified into thymic-derived Tregs (tTregs), endogenous-induced Tregs (pTregs), which are produced by antigen-stimulated T cells in the periphery in vivo, and induced Tregs (iTregs), which differentiate from naïve T cells in vitro. In recent years, studies have found that Tregs are divided into lymphatic and tissue-resident Tregs according to their location. Research on the generation and function of lymphoid Tregs has been more comprehensive and thorough, but the role of tissue Tregs is still in the exploratory stage, and it has become a research hot spot. In this review, we discuss the instability and plasticity of Tregs and the latest developments of tissue-resident Tregs in the field of biology, including adipose tissue, colon, skeletal muscle, and other Tregs that have been recently discovered as well as their production, regulation, and function in specific tissues and their role in the pathogenesis of autoimmune diseases.

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

2000 ◽  
Vol 11 (11) ◽  
pp. 3805-3817 ◽  
Author(s):  
Aikaterini Kontrogianni-Konstantopoulos ◽  
Shu-Ching Huang ◽  
Edward J. Benz
Keyword(s):  
Skeletal Muscle ◽  
Protein S ◽  
Binding Assays ◽  
Adult Skeletal Muscle ◽  
Exon 2 ◽  
Alternatively Spliced ◽  
Translation Initiation Codon ◽  
Protein 4.1R

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.

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

2015 ◽  
Vol 13 (1) ◽  
pp. nrs.13005 ◽  
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.

The extracellular matrix of the developing cornea: diversity, deposition and function*

Development ◽  
1988 ◽  
Vol 103 (Supplement) ◽  
pp. 195-205
Author(s):  
J. B. L. Bard ◽  
M. K. Bansal ◽  
A. S. A. Ross
Keyword(s):  
Extracellular Matrix ◽  
Chondroitin Sulphate ◽  
Corneal Stroma ◽  
Experimental System ◽  
Collagen I ◽  
And Function ◽  
20 Nm

This paper examines the role of the extracellular matrix (ECM) in the development of the cornea. After a brief summary of the corneal structure and ECM, we describe evidence suggesting that the differentiation of neural crest (NC) cells into endothelium and fibroblasts is under the control of ocular ECM. We then examine the role of collagen I in stromal morphogenesis by comparing normal corneas with those of homozygous Movl3 mice which do not make collagen I. We report that, in spite of this absence, the cellular morphology of the Movl3 eye is indistinguishable from that of the wild type. In the 16-day mutant stroma, however, the remaining collagens form small amounts of disorganized, thin fibrils rather than orthogonally organized 20 nm-diameter fibrils; a result implying that collagen I plays only a structural role and that its absence is not compensated for. It also suggests that, because these remaining collagens will not form the normal fibrils that they will in vitro, fibrillogenesis in the corneal stroma differs from that elsewhere. The latter part of the paper describes our current work on chick stromal deposition using corneal epithelia isolated with an intact basal lamina that lay down in vitro ∼3μm-thick stromas of organized fibrils similar to that seen in vivo. This experimental system has yielded two unexpected results. First, the amount of collagen and proteoglycans produced by such epithelia is not dependent on whether its substratum is collagenous and we therefore conclude that stromal production by the intact epithelium is more autonomous than hitherto thought. Second, chondroitin sulphate (CS), the predominant proteoglycan, appears to play no role in stromal morphogenesis: epithelia cultured in testicular hyaluronidase, which degrades CS, lay down stromas whose organization and fibrildiameter distribution are indistinguishable from controls. One possible role for CS, however, is as a lubricant which facilitates corneal growth: it could allow fibrils to move over one another without deforming their orthogonal organization. Finally, we have examined the processes of fibrillogenesis in the corneal stroma and conclude that they are different from those elsewhere in the embryo and in vitro, perhaps because there is in the primary stroma an unidentified, highly hydrated ECM macromolecule that embeds the fibrils and that may mediate their morphogenesis.

scholarly journals Characterization and function of Ca2+-activated K+ channels in arteriolar muscle cells

1998 ◽  
Vol 274 (1) ◽  
pp. H27-H34 ◽  
Author(s):  
William F. Jackson ◽  
Kevin L. Blair
Keyword(s):  
Single Channel ◽  
Muscle Cells ◽  
Hill Coefficient ◽  
Apparent Lack ◽  
Maximal Activation ◽  
And Function ◽  
Resting Tone

We examined the functional role of large-conductance Ca2+-activated K+(KCa) channels in the hamster cremasteric microcirculation by intravital videomicroscopy and characterized the single-channel properties of these channels in inside-out patches of membrane from enzymatically isolated cremasteric arteriolar muscle cells. In second-order (39 ± 1 μm, n = 8) and third-order (19 ± 2 μm, n = 8) cremasteric arterioles with substantial resting tone, superfusion with the KCa channel antagonists tetraethylammonium (TEA, 1 mM) or iberiotoxin (IBTX, 100 nM) had no significant effect on resting diameters ( P > 0.05). However, TEA potentiated O2-induced arteriolar constriction in vivo, and IBTX enhanced norepinephrine-induced contraction of cremasteric arteriolar muscle cells in vitro. Patch-clamp studies revealed unitary K+-selective and IBTX-sensitive currents with a single-channel conductance of 240 ± 2 pS between −60 and 60 mV ( n = 7 patches) in a symmetrical 140 mM K+ gradient. The free Ca2+ concentration ([Ca2+]) for half-maximal channel activation was 44 ± 3, 20 ± 1, 6 ± 0.4, and 3 ± 0.5 μM at membrane potentials of −60, −30, +30, and +60 mV, respectively ( n = 5), with a Hill coefficient of 1.9 ± 0.2. Channel activity increased e-fold for a 16 ± 1 mV ( n = 6) depolarization. The plot of log[Ca2+] vs. voltage for half-maximal activation ( V ½) was linear ( r 2 = 0.9843, n = 6); the change in V ½ for a 10-fold change in [Ca2+] was 84 ± 5 mV, and the [Ca2+] for half-maximal activation at 0 mV (Ca0; the Ca2+ set point) was 9 μM. Thus, in vivo, KCa channels are silent in cremasteric arterioles at rest but can be recruited during vasoconstriction. We propose that the high Ca0 is responsible for the apparent lack of activity of these channels in resting cremasteric arterioles, and we suggest that this may result from expression of unique KCa channels in the microcirculation.

PSGL-1 regulates platelet P-selectin-mediated endothelial activation and shedding of P-selectin from activated platelets

2007 ◽  
Vol 98 (10) ◽  
pp. 806-812 ◽  
Author(s):  
Vandana Dole ◽  
Wolfgang Bergmeier ◽  
Ian Patten ◽  
Junichi Hirahashi ◽  
Tanya Mayadas ◽  
...  
Keyword(s):  
Endothelial Activation ◽  
Leukocyte Rolling ◽  
Wild Type ◽  
Platelet Surface ◽  
Activated Platelets ◽  
And Function ◽  
Body Secretion

SummaryWe have previously shown that activated platelets in circulation stimulate release of endothelial Weibel-Palade bodies thus increasing leukocyte rolling in venules. P-selectin on the activated platelets mediates adhesion to leukocytes via PSGL-1 and is rapidly shed into plasma. We were interested in studying the role of PSGL-1 in regulating expression and function of platelet P-selectin. We show here that PSGL-1 is critical for the activation of endothelial cells in venules of mice infused with activated platelets. The interaction of platelet P-selectin with PSGL-1 is also required for P-selectin shedding, as P-selectin was retained significantly longer on the surface of activated platelets infused into PSGL-1-/- compared to wild-type mice. The leukocyte integrin αMβ2 (Mac-1) was not required for P-selectin shedding. In addition to shedding, P-selectin can be downregulated from the platelet surface through internalization and this is the predominant mechanism in the absence of PSGL-1. We demonstrate that leukocyte- neutrophil elastase,known to cleave P-selectin in vitro, is not the major sheddase for P-selectin in vivo. In conclusion, interaction of platelet P-selectin with PSGL-1 is crucial for activation of the endothelium andWeibel-Palade body secretion. The interaction with PSGL-1 also results in rapid shedding of P-selectin thus downregulating the inflammatory potential of the platelet.

scholarly journals Talin is required for integrin-mediated platelet function in hemostasis and thrombosis

2007 ◽  
Vol 204 (13) ◽  
pp. 3103-3111 ◽  
Author(s):  
Brian G. Petrich ◽  
Patrizia Marchese ◽  
Zaverio M. Ruggeri ◽  
Saskia Spiess ◽  
Rachel A.M. Weichert ◽  
...  
Keyword(s):  
Platelet Adhesion ◽  
Ex Vivo ◽  
Focal Adhesions ◽  
Β1 Integrin ◽  
Normal Morphology ◽  
And Function ◽  
Specific Deletion

Integrins are critical for hemostasis and thrombosis because they mediate both platelet adhesion and aggregation. Talin is an integrin-binding cytoplasmic adaptor that is a central organizer of focal adhesions, and loss of talin phenocopies integrin deletion in Drosophila. Here, we have examined the role of talin in mammalian integrin function in vivo by selectively disrupting the talin1 gene in mouse platelet precursor megakaryocytes. Talin null megakaryocytes produced circulating platelets that exhibited normal morphology yet manifested profoundly impaired hemostatic function. Specifically, platelet-specific deletion of talin1 led to spontaneous hemorrhage and pathological bleeding. Ex vivo and in vitro studies revealed that loss of talin1 resulted in dramatically impaired integrin αIIbβ3-mediated platelet aggregation and β1 integrin–mediated platelet adhesion. Furthermore, loss of talin1 strongly inhibited the activation of platelet β1 and β3 integrins in response to platelet agonists. These data establish that platelet talin plays a crucial role in hemostasis and provide the first proof that talin is required for the activation and function of mammalian α2β1 and αIIbβ3 integrins in vivo.

scholarly journals IL-4 and SDF-1 Increase Adipose Tissue-Derived Stromal Cell Ability to Improve Rat Skeletal Muscle Regeneration

2020 ◽  
Vol 21 (9) ◽  
pp. 3302
Author(s):  
Małgorzata Zimowska ◽  
Karolina Archacka ◽  
Edyta Brzoska ◽  
Joanna Bem ◽  
Areta M. Czerwinska ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Adipose Tissue ◽  
Muscle Regeneration ◽  
Structure And Function ◽  
Skeletal Muscle Regeneration ◽  
Stem Cell Markers ◽  
Myogenic Factors ◽  
And Function

Skeletal muscle regeneration depends on the satellite cells, which, in response to injury, activate, proliferate, and reconstruct damaged tissue. However, under certain conditions, such as large injuries or myopathies, these cells might not sufficiently support repair. Thus, other cell populations, among them adipose tissue-derived stromal cells (ADSCs), are tested as a tool to improve regeneration. Importantly, the pro-regenerative action of such cells could be improved by various factors. In the current study, we tested whether IL-4 and SDF-1 could improve the ability of ADSCs to support the regeneration of rat skeletal muscles. We compared their effect at properly regenerating fast-twitch EDL and poorly regenerating slow-twitch soleus. To this end, ADSCs subjected to IL-4 and SDF-1 were analyzed in vitro and also in vivo after their transplantation into injured muscles. We tested their proliferation rate, migration, expression of stem cell markers and myogenic factors, their ability to fuse with myoblasts, as well as their impact on the mass, structure and function of regenerating muscles. As a result, we showed that cytokine-pretreated ADSCs had a beneficial effect in the regeneration process. Their presence resulted in improved muscle structure and function, as well as decreased fibrosis development and a modulated immune response.

scholarly journals The N-Terminus ofDictyosteliumScar Interacts with Abi and HSPC300 and Is Essential for Proper Regulation and Function

2007 ◽  
Vol 18 (5) ◽  
pp. 1609-1620 ◽  
Author(s):  
Diana Caracino ◽  
Cheryl Jones ◽  
Mark Compton ◽  
Charles L. Saxe
Keyword(s):  
Actin Polymerization ◽  
Terminal Region ◽  
Wild Type ◽  
Large Molecular Weight ◽  
Weight Protein ◽  
And Function ◽  
Necessary And Sufficient

Scar/WAVE proteins, members of the conserved Wiskott-Aldrich syndrome (WAS) family, promote actin polymerization by activating the Arp2/3 complex. A number of proteins, including a complex containing Nap1, PIR121, Abi1/2, and HSPC300, interact with Scar/WAVE, though the role of this complex in regulating Scar function remains unclear. Here we identify a short N-terminal region of Dictyostelium Scar that is necessary and sufficient for interaction with HSPC300 and Abi in vitro. Cells expressing Scar lacking this N-terminal region show abnormalities in F-actin distribution, cell morphology, movement, and cytokinesis. This is true even in the presence of wild-type Scar. The data suggest that the first 96 amino acids of Scar are necessary for participation in a large-molecular-weight protein complex, and that this Scar-containing complex is responsible for the proper localization and regulation of Scar. The presence of mis-regulated or unregulated Scar has significant deleterious effects on cells and may explain the need to keep Scar activity tightly controlled in vivo either by assembly in a complex or by rapid degradation.

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