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Activation of serum/glucocorticoid-induced kinase 1 (SGK1) is important to maintain skeletal muscle homeostasis and prevent atrophy.

Andres-Mateos E, Brinkmeier H, Burks TN, Mejias R, Files DC, Steinberger M, Soleimani A, Marx R, Simmers JL, Lin B, Finanger Hedderick E, Marr TG, Lin BM, Hourdé C, Leinwand LA, Kuhl D, Föller M, Vogelsang S, Hernandez-Diaz I, Vaughan DK, Alvarez de la Rosa D, Lang F, Cohn RD - EMBO Mol Med (2012)

Bottom Line: Here, we describe a mechanism underlying muscle preservation and translate it to non-hibernating mammals.Although Akt has an established role in skeletal muscle homeostasis, we find that serum- and glucocorticoid-inducible kinase 1 (SGK1) regulates muscle mass maintenance via downregulation of proteolysis and autophagy as well as increased protein synthesis during hibernation.Our results identify a novel therapeutic target to combat loss of skeletal muscle mass associated with muscle degeneration and atrophy.

View Article: PubMed Central - PubMed

Affiliation: McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, USA.

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Electroporation of constitutively active Sgk1 protects against immobilization atrophyTransfection of constitutively active Sgk1 (CA) into immobilized tibialis anterior muscle (green) reveals increased fiber size diameter when compared to control, EGFP only transfected muscle fibers of immobilized tibialis anterior muscles (100 µm). Laminin γ-1 staining (red) outlines the basement membrane and blue staining marks nuclei (DAPI).Representation of the minimum Feret's diameter average ± SD (control and immobilized; n = 9–10 per group; 800–950 fibers were measured) (*p = 0.029, *p = 0.034, *p = 0.047, p = 0.43, respectively).Percentage distribution of the minimum Feret's diameter of tibialis anterior muscle immobilized and transfected with eGFP (GFP), wild-type Sgk1 (WT), kinase dead Sgk1 (KD) and constitutively active Sgk1 (CA) compared to non-immobilized control TA muscle (black dotted line).Schematic representation of pathways involved in the preservation of skeletal muscle mass during prolonged periods of immobilization. SGK1, in addition to Akt, mediates protein degradation via phosphorylation of Foxo3a, with the subsequent inhibition of proteolysis and autophagy and protein synthesis through the activation of mTOR.
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fig07: Electroporation of constitutively active Sgk1 protects against immobilization atrophyTransfection of constitutively active Sgk1 (CA) into immobilized tibialis anterior muscle (green) reveals increased fiber size diameter when compared to control, EGFP only transfected muscle fibers of immobilized tibialis anterior muscles (100 µm). Laminin γ-1 staining (red) outlines the basement membrane and blue staining marks nuclei (DAPI).Representation of the minimum Feret's diameter average ± SD (control and immobilized; n = 9–10 per group; 800–950 fibers were measured) (*p = 0.029, *p = 0.034, *p = 0.047, p = 0.43, respectively).Percentage distribution of the minimum Feret's diameter of tibialis anterior muscle immobilized and transfected with eGFP (GFP), wild-type Sgk1 (WT), kinase dead Sgk1 (KD) and constitutively active Sgk1 (CA) compared to non-immobilized control TA muscle (black dotted line).Schematic representation of pathways involved in the preservation of skeletal muscle mass during prolonged periods of immobilization. SGK1, in addition to Akt, mediates protein degradation via phosphorylation of Foxo3a, with the subsequent inhibition of proteolysis and autophagy and protein synthesis through the activation of mTOR.

Mentions: In order to assess whether SGK1 expression protects against targeted disuse atrophy, we transfected TA muscles via electroporation with plasmids encoding Sgk1 WT (Sgk1WT), Kinase Dead (Sgk1KD) and Constitutively Active Sgk1 (Sgk1CA) all fused to EGFP. One hindlimb was immobilized by stapling (Burks et al, 2011), and the plasmids were injected into both the immobilized and the contralateral non-immobilized muscles. After 9 days, both TA muscles were assessed for plasmid expression and morphometric measurements. Co-immunostaining for laminin γ-1 ensured that plasmid expression was confined to skeletal muscle fibers and not within extracellular space. Gene transfection efficiency was determined by calculating the cross sectional area of GFP positive muscle fibers expressed as a percentage of the total cross sectional area (Schertzer et al, 2006). All constructs revealed a transfection efficiency of 58.6–78.5% (Supporting Information Fig S6D). Transfection of contralateral, non-immobilized TA muscles did not show any significant changes in muscle fiber size or morphology with any of the plasmids injected (Supporting Information Fig S6B). However, in the immobilized limb transfection of Sgk1CA completely prevented muscle atrophy when compared to GFP only, Sgk1WT and Sgk1KD (Fig 7A–C and Supporting Information Fig S6A). Importantly, skeletal muscle atrophy was only prevented by transfection of the constitutively active form of Sgk1.


Activation of serum/glucocorticoid-induced kinase 1 (SGK1) is important to maintain skeletal muscle homeostasis and prevent atrophy.

Andres-Mateos E, Brinkmeier H, Burks TN, Mejias R, Files DC, Steinberger M, Soleimani A, Marx R, Simmers JL, Lin B, Finanger Hedderick E, Marr TG, Lin BM, Hourdé C, Leinwand LA, Kuhl D, Föller M, Vogelsang S, Hernandez-Diaz I, Vaughan DK, Alvarez de la Rosa D, Lang F, Cohn RD - EMBO Mol Med (2012)

Electroporation of constitutively active Sgk1 protects against immobilization atrophyTransfection of constitutively active Sgk1 (CA) into immobilized tibialis anterior muscle (green) reveals increased fiber size diameter when compared to control, EGFP only transfected muscle fibers of immobilized tibialis anterior muscles (100 µm). Laminin γ-1 staining (red) outlines the basement membrane and blue staining marks nuclei (DAPI).Representation of the minimum Feret's diameter average ± SD (control and immobilized; n = 9–10 per group; 800–950 fibers were measured) (*p = 0.029, *p = 0.034, *p = 0.047, p = 0.43, respectively).Percentage distribution of the minimum Feret's diameter of tibialis anterior muscle immobilized and transfected with eGFP (GFP), wild-type Sgk1 (WT), kinase dead Sgk1 (KD) and constitutively active Sgk1 (CA) compared to non-immobilized control TA muscle (black dotted line).Schematic representation of pathways involved in the preservation of skeletal muscle mass during prolonged periods of immobilization. SGK1, in addition to Akt, mediates protein degradation via phosphorylation of Foxo3a, with the subsequent inhibition of proteolysis and autophagy and protein synthesis through the activation of mTOR.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3569655&req=5

fig07: Electroporation of constitutively active Sgk1 protects against immobilization atrophyTransfection of constitutively active Sgk1 (CA) into immobilized tibialis anterior muscle (green) reveals increased fiber size diameter when compared to control, EGFP only transfected muscle fibers of immobilized tibialis anterior muscles (100 µm). Laminin γ-1 staining (red) outlines the basement membrane and blue staining marks nuclei (DAPI).Representation of the minimum Feret's diameter average ± SD (control and immobilized; n = 9–10 per group; 800–950 fibers were measured) (*p = 0.029, *p = 0.034, *p = 0.047, p = 0.43, respectively).Percentage distribution of the minimum Feret's diameter of tibialis anterior muscle immobilized and transfected with eGFP (GFP), wild-type Sgk1 (WT), kinase dead Sgk1 (KD) and constitutively active Sgk1 (CA) compared to non-immobilized control TA muscle (black dotted line).Schematic representation of pathways involved in the preservation of skeletal muscle mass during prolonged periods of immobilization. SGK1, in addition to Akt, mediates protein degradation via phosphorylation of Foxo3a, with the subsequent inhibition of proteolysis and autophagy and protein synthesis through the activation of mTOR.
Mentions: In order to assess whether SGK1 expression protects against targeted disuse atrophy, we transfected TA muscles via electroporation with plasmids encoding Sgk1 WT (Sgk1WT), Kinase Dead (Sgk1KD) and Constitutively Active Sgk1 (Sgk1CA) all fused to EGFP. One hindlimb was immobilized by stapling (Burks et al, 2011), and the plasmids were injected into both the immobilized and the contralateral non-immobilized muscles. After 9 days, both TA muscles were assessed for plasmid expression and morphometric measurements. Co-immunostaining for laminin γ-1 ensured that plasmid expression was confined to skeletal muscle fibers and not within extracellular space. Gene transfection efficiency was determined by calculating the cross sectional area of GFP positive muscle fibers expressed as a percentage of the total cross sectional area (Schertzer et al, 2006). All constructs revealed a transfection efficiency of 58.6–78.5% (Supporting Information Fig S6D). Transfection of contralateral, non-immobilized TA muscles did not show any significant changes in muscle fiber size or morphology with any of the plasmids injected (Supporting Information Fig S6B). However, in the immobilized limb transfection of Sgk1CA completely prevented muscle atrophy when compared to GFP only, Sgk1WT and Sgk1KD (Fig 7A–C and Supporting Information Fig S6A). Importantly, skeletal muscle atrophy was only prevented by transfection of the constitutively active form of Sgk1.

Bottom Line: Here, we describe a mechanism underlying muscle preservation and translate it to non-hibernating mammals.Although Akt has an established role in skeletal muscle homeostasis, we find that serum- and glucocorticoid-inducible kinase 1 (SGK1) regulates muscle mass maintenance via downregulation of proteolysis and autophagy as well as increased protein synthesis during hibernation.Our results identify a novel therapeutic target to combat loss of skeletal muscle mass associated with muscle degeneration and atrophy.

View Article: PubMed Central - PubMed

Affiliation: McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, USA.

Show MeSH
Related in: MedlinePlus