scholarly journals The exocyst complex regulates insulin-stimulated glucose uptake of skeletal muscle cells

2019 ◽  
Vol 317 (6) ◽  
pp. E957-E972
Author(s):  
Brent A. Fujimoto ◽  
Madison Young ◽  
Lamar Carter ◽  
Alina P. S. Pang ◽  
Michael J. Corley ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Plasma Membrane ◽  
Cell Surface ◽  
Glucose Uptake ◽  
Glucose Transporter ◽  
Muscle Cells ◽  
Skeletal Muscle Cells ◽  
Cell Surface Receptor ◽  
Exocyst Complex

Skeletal muscle handles ~80–90% of the insulin-induced glucose uptake. In skeletal muscle, insulin binding to its cell surface receptor triggers redistribution of intracellular glucose transporter GLUT4 protein to the cell surface, enabling facilitated glucose uptake. In adipocytes, the eight-protein exocyst complex is an indispensable constituent in insulin-induced glucose uptake, as it is responsible for the targeted trafficking and plasma membrane-delivery of GLUT4. However, the role of the exocyst in skeletal muscle glucose uptake has never been investigated. Here we demonstrate that the exocyst is a necessary factor in insulin-induced glucose uptake in skeletal muscle cells as well. The exocyst complex colocalizes with GLUT4 storage vesicles in L6-GLUT4myc myoblasts at a basal state and associates with these vesicles during their translocation to the plasma membrane after insulin signaling. Moreover, we show that the exocyst inhibitor endosidin-2 and a heterozygous knockout of Exoc5 in skeletal myoblast cells both lead to impaired GLUT4 trafficking to the plasma membrane and hinder glucose uptake in response to an insulin stimulus. Our research is the first to establish that the exocyst complex regulates insulin-induced GLUT4 exocytosis and glucose metabolism in muscle cells. A deeper knowledge of the role of the exocyst complex in skeletal muscle tissue may help our understanding of insulin resistance in type 2 diabetes.

scholarly journals Fish Glucose Transporter (GLUT)-4 Differs from Rat GLUT4 in Its Traffic Characteristics but Can Translocate to the Cell Surface in Response to Insulin in Skeletal Muscle Cells

Endocrinology ◽  
2007 ◽  
Vol 148 (11) ◽  
pp. 5248-5257 ◽  
Author(s):  
Mònica Díaz ◽  
Costin N. Antonescu ◽  
Encarnación Capilla ◽  
Amira Klip ◽  
Josep V. Planas
Keyword(s):  
Skeletal Muscle ◽  
Plasma Membrane ◽  
Cell Surface ◽  
Glucose Uptake ◽  
Brown Trout ◽  
Glucose Transporter ◽  
Intracellular Localization ◽  
Muscle Cells ◽  
Skeletal Muscle Cells ◽  
Glut 4

In mammals, glucose transporter (GLUT)-4 plays an important role in glucose homeostasis mediating insulin action to increase glucose uptake in insulin-responsive tissues. In the basal state, GLUT4 is located in intracellular compartments and upon insulin stimulation is recruited to the plasma membrane, allowing glucose entry into the cell. Compared with mammals, fish are less efficient restoring plasma glucose after dietary or exogenous glucose administration. Recently our group cloned a GLUT4-homolog in skeletal muscle from brown trout (btGLUT4) that differs in protein motifs believed to be important for endocytosis and sorting of mammalian GLUT4. To study the traffic of btGLUT4, we generated a stable L6 muscle cell line overexpressing myc-tagged btGLUT4 (btGLUT4myc). Insulin stimulated btGLUT4myc recruitment to the cell surface, although to a lesser extent than rat-GLUT4myc, and enhanced glucose uptake. Interestingly, btGLUT4myc showed a higher steady-state level at the cell surface under basal conditions than rat-GLUT4myc due to a higher rate of recycling of btGLUT4myc and not to a slower endocytic rate, compared with rat-GLUT4myc. Furthermore, unlike rat-GLUT4myc, btGLUT4myc had a diffuse distribution throughout the cytoplasm of L6 myoblasts. In primary brown trout skeletal muscle cells, insulin also promoted the translocation of endogenous btGLUT4 to the plasma membrane and enhanced glucose transport. Moreover, btGLUT4 exhibited a diffuse intracellular localization in unstimulated trout myocytes. Our data suggest that btGLUT4 is subjected to a different intracellular traffic from rat-GLUT4 and may explain the relative glucose intolerance observed in fish.

ALY688 elicits adiponectin-mimetic signaling and improves insulin action in skeletal muscle cells

2021 ◽  
Author(s):  
Hye Kyoung Sung ◽  
Patricia L. Mitchell ◽  
Sean Gross ◽  
Andre Marette ◽  
Gary Sweeney
Keyword(s):  
Skeletal Muscle ◽  
Insulin Sensitivity ◽  
Glucose Uptake ◽  
Glucose Transporter ◽  
Muscle Cells ◽  
Temporal Analysis ◽  
Skeletal Muscle Cells ◽  
Adiponectin Receptor ◽  
Metabolic Effects

Adiponectin is well established to mediate many beneficial metabolic effects, and this has stimulated great interest in development and validation of adiponectin receptor agonists as pharmaceutical tools. This study investigated the effects of ALY688, a peptide-based adiponectin receptor agonist, in rat L6 skeletal muscle cells. ALY688 significantly increased phosphorylation of several adiponectin downstream effectors, including AMPK, ACC and p38MAPK, assessed by immunoblotting and immunofluorescence microscopy. Temporal analysis using cells expressing an Akt biosensor demonstrated that ALY688 enhanced insulin sensitivity. This effect was associated with increased insulin-stimulated Akt and IRS-1 phosphorylation. The functional metabolic significance of these signaling effects was examined by measuring glucose uptake in myoblasts stably overexpressing the glucose transporter GLUT4. ALY688 treatment both increased glucose uptake itself and enhanced insulin-stimulated glucose uptake. In the model of high glucose/high insulin (HGHI)-induced insulin resistant cells, both temporal studies using the Akt biosensor as well as immunoblotting assessing Akt and IRS-1 phosphorylation indicated that ALY688 significantly reduced insulin resistance. Importantly, we observed that ALY688 administration to high-fat high sucrose fed mice also improve glucose handling, validating its efficacy in vivo. In summary, these data indicate that ALY688 activates adiponectin signaling pathways in skeletal muscle, leading to improved insulin sensitivity and beneficial metabolic effects.

scholarly journals 1-Deoxysphingolipids, Early Predictors of Type 2 Diabetes, Compromise the Functionality of Skeletal Myoblasts

2021 ◽  
Vol 12 ◽  
Author(s):  
Duyen Tran ◽  
Stephen Myers ◽  
Courtney McGowan ◽  
Darren Henstridge ◽  
Rajaraman Eri ◽  
...  
Keyword(s):  
Type 2 Diabetes ◽  
Skeletal Muscle ◽  
Glucose Uptake ◽  
Muscle Cells ◽  
Skeletal Muscle Cells ◽  
Muscle Dysfunction ◽  
Dependent Manner

Metabolic dysfunction, dysregulated differentiation, and atrophy of skeletal muscle occur as part of a cluster of abnormalities associated with the development of Type 2 diabetes mellitus (T2DM). Recent interest has turned to the attention of the role of 1-deoxysphingolipids (1-DSL), atypical class of sphingolipids which are found significantly elevated in patients diagnosed with T2DM but also in the asymptomatic population who later develop T2DM. In vitro studies demonstrated that 1-DSL have cytotoxic properties and compromise the secretion of insulin from pancreatic beta cells. However, the role of 1-DSL on the functionality of skeletal muscle cells in the pathophysiology of T2DM still remains unclear. This study aimed to investigate whether 1-DSL are cytotoxic and disrupt the cellular processes of skeletal muscle precursors (myoblasts) and differentiated cells (myotubes) by performing a battery of in vitro assays including cell viability adenosine triphosphate assay, migration assay, myoblast fusion assay, glucose uptake assay, and immunocytochemistry. Our results demonstrated that 1-DSL significantly reduced the viability of myoblasts in a concentration and time-dependent manner, and induced apoptosis as well as cellular necrosis. Importantly, myoblasts were more sensitive to the cytotoxic effects induced by 1-DSL rather than by saturated fatty acids, such as palmitate, which are critical mediators of skeletal muscle dysfunction in T2DM. Additionally, 1-DSL significantly reduced the migration ability of myoblasts and the differentiation process of myoblasts into myotubes. 1-DSL also triggered autophagy in myoblasts and significantly reduced insulin-stimulated glucose uptake in myotubes. These findings demonstrate that 1-DSL directly compromise the functionality of skeletal muscle cells and suggest that increased levels of 1-DSL observed during the development of T2DM are likely to contribute to the pathophysiology of muscle dysfunction detected in this disease.

The Exocyst Complex in Insulin-Stimulated Glucose Uptake in Skeletal Muscle Cells

Diabetes ◽  
2018 ◽  
Vol 67 (Supplement 1) ◽  
pp. 241-LB
Author(s):  
BRENT FUJIMOTO ◽  
AMANDA LEE ◽  
ADRIAN M. WONG ◽  
LAMAR T. CARTER ◽  
BEN FOGELGREN ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Glucose Uptake ◽  
Muscle Cells ◽  
Skeletal Muscle Cells ◽  
Exocyst Complex

scholarly journals The Proinflammatory Cytokine Tumor Necrosis Factor-α Increases the Amount of Glucose Transporter-4 at the Surface of Muscle Cells Independently of Changes in Interleukin-6

Endocrinology ◽  
2007 ◽  
Vol 149 (4) ◽  
pp. 1880-1889 ◽  
Author(s):  
Nerea Roher ◽  
Victor Samokhvalov ◽  
Mònica Díaz ◽  
Simon MacKenzie ◽  
Amira Klip ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Cell Surface ◽  
Glucose Uptake ◽  
Proinflammatory Cytokine ◽  
Glucose Transporter ◽  
De Novo ◽  
Muscle Cells ◽  
Nuclear Factor Κb ◽  
Nuclear Factor ◽  
Insulin Resistant

TNFα is a proinflammatory cytokine secreted by macrophages in response to bacterial infection. Recently new evidence has emerged suggesting that stressed or injured myocytes produce TNFα that then acts as an autocrine and/or paracrine mediator. TNFα receptors types 1 and 2 are present in skeletal muscle cells, and muscle cells can secrete, in addition to TNFα, other cytokines such as IL-1β or IL-6. Furthermore, the plasma concentration of TNFα is elevated in insulin-resistant states associated with obesity and type 2 diabetes. Here we show that TNFα increased the amount of glucose transporter (GLUT)-4 at the plasma membrane and also glucose uptake in the L6 muscle cell line stably expressing GLUT4 tagged with the c-myc epitope. Regardless of the state of differentiation of the L6 cells, TNFα did not affect the rate of proliferation or of apoptosis. The stimulatory effects of TNFα on cell surface GLUT4 and glucose uptake were blocked by nuclear factor-κB and p38MAPK pathway specific inhibitors (Bay 11-7082 and SB220025), and these two pathways were stimulated by TNFα. Furthermore, although TNFα increased IL-6 mRNA and protein expression, IL-6 did not mediate the effects of TNFα on cell surface GLUT4 levels, which also did not require de novo protein synthesis. The results indicate that TNFα can stimulate glucose uptake in L6 muscle cells by inducing GLUT4 translocation to the plasma membrane, possibly through activation of the nuclear factor-κB and p38MAPK signaling pathways and independently of the production of IL-6.

scholarly journals β-Sitosterol-D-Glucopyranoside Mimics Estrogenic Properties and Stimulates Glucose Utilization in Skeletal Muscle Cells

Molecules ◽  
2021 ◽  
Vol 26 (11) ◽  
pp. 3129
Author(s):  
Jyotsana Pandey ◽  
Kapil Dev ◽  
Sourav Chattopadhyay ◽  
Sleman Kadan ◽  
Tanuj Sharma ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Glucose Uptake ◽  
Glucose Utilization ◽  
Diabetes Management ◽  
Expression System ◽  
Muscle Cells ◽  
Skeletal Muscle Cells ◽  
Cell Periphery ◽  
Glut4 Translocation ◽  
In Silico Docking

Estrogenic molecules have been reported to regulate glucose homeostasis and may be beneficial for diabetes management. Here, we investigated the estrogenic effect of β-sitosterol-3-O-D-glucopyranoside (BSD), isolated from the fruits of Cupressus sempervirens and monitored its ability to regulate glucose utilization in skeletal muscle cells. BSD stimulated ERE-mediated luciferase activity in both ERα and ERβ-ERE luc expression system with greater response through ERβ in HEK-293T cells, and induced the expression of estrogen-regulated genes in estrogen responsive MCF-7 cells. In silico docking and molecular interaction studies revealed the affinity and interaction of BSD with ERβ through hydrophobic interaction and hydrogen bond pairing. Furthermore, prolonged exposure of L6-GLUT4myc myotubes to BSD raised the glucose uptake under basal conditions without affecting the insulin-stimulated glucose uptake, the effect associated with enhanced translocation of GLUT4 to the cell periphery. The BSD-mediated biological response to increase GLUT4 translocation was obliterated by PI-3-K inhibitor wortmannin, and BSD significantly increased the phosphorylation of AKT (Ser-473). Moreover, BSD-induced GLUT4 translocation was prevented in the presence of fulvestrant. Our findings reveal the estrogenic activity of BSD to stimulate glucose utilization in skeletal muscle cells via PI-3K/AKT-dependent mechanism.

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